Semiconductor device, display device, and electronic device

ABSTRACT

To provide a semiconductor device which operates stably with few malfunctions due to noise, with low power consumption, and little variation in characteristics; a display device including the semiconductor device; and an electronic device including the display device. An output terminal is connected to a power supply line, thereby reducing variation in electric potential of the output terminal. In addition, a gate electrode potential which turns ON a transistor is maintained due to the capacitance of the transistor. Further, change in characteristics of the transistor is reduced by a signal line for reverse bias.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/960,709, filed Dec. 6, 2010, now allowed, which is a divisional ofU.S. application Ser. No. 12/244,348, filed Oct. 2, 2008, now U.S. Pat.No. 7,847,593, which is a divisional of U.S. application Ser. No.11/612,217, filed Dec. 18, 2006, now U.S. Pat. No. 7,432,737, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2005-378262 on Dec. 28, 2005, all of which are incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, a displaydevice, and an electronic device.

2. Description of the Related Art

A shift register circuit is a circuit which operates such that contentthereof is shifted by one stage each time a pulse is applied. Utilizingthis property, shift registers are used in circuits for mutualconversion of serial signals and parallel signals. Such circuits whichconvert serial signals to parallel signals, or convert parallel signalsto serial signals are mainly used for networks having circuits connectedto each other. The number of transmission paths for connecting circuitsto each other and transmitting signals in a network is often smallrelative to the amount of data to be transmitted. In such cases,parallel signals are converted into serial signals in a transmittercircuit and are sequentially sent to a transmission path, and serialsignals that have been sequentially sent are converted into parallelsignals in a receiver circuit. Thus, signals can be exchanged using asmall number of transmission paths.

A display device display images by controlling the luminance of eachpixel in accordance with image signals inputted from the outside. Here,since it is difficult to use a number of transmission paths of imagesignals from the outside that is equivalent to the number of pixels, itis necessary to subject the image signals to serial-parallel conversion.Therefore, shift registers are used in both a circuit which transmitsimage signals to the display device and a circuit for driving thedisplay device which receives the image signals.

A CMOS circuit combining an n-channel transistor and a p-channeltransistor is usually used in the above-described shift registercircuit. However, in order to form a CMOS circuit combining an n-channeltransistor and a p-channel transistor over the same substrate, it isnecessary to form transistors having conductivity types opposite to eachother over the same substrate, so the manufacturing process inevitablybecomes complex. Consequently, increase in cost or decrease in yield ofsemiconductor devices results.

Therefore, a circuit having transistors which all have the same polarity(also referred to as a unipolar circuit) has been devised. A unipolarcircuit makes it possible to omit some of the steps in the manufacturingprocess, such as the step of adding an impurity element. Thereby,increase in cost and decrease in yield can be suppressed.

For example, consider the case of forming a logic circuit in which allthe transistors have n-channel polarity. This circuit has a problem inthat when a potential with a high potential power supply is outputted,in accordance with the threshold of the n-channel transistors, voltageof an output signal is attenuated compared to voltage of an inputsignal. Therefore, a circuit called a bootstrap circuit is widely usedso that the voltage of an output signal is not attenuated. A bootstrapcircuit is realized when the gate electrode of a transistor capacitivelycoupled with an output terminal is floated after a transistor connectedto the high potential power supply is turned ON so that current beginsflowing through a channel. Thus, the electric potential of the outputterminal rises and the electric potential of the gate electrode of thetransistor also rises correspondingly, so as to eventually exceed thepotential of the high potential power supply plus the threshold voltageof the transistor. Thereby, the potential of the output terminal can bemade almost equivalent to the potential of the high potential powersupply.

Using such a bootstrap circuit, a semiconductor device in which outputpotential is not attenuated even in the case of using a unipolartransistor can be realized. Further, a shift register circuit can beformed using the bootstrap circuit (for example, Reference 1: JapanesePublished Patent Application No. 2002-215118 and Reference 2: SID2005,p. 1050, “An Improved Dynamic Ratio Less Shift Register Circuit Suitablefor LTPS-TFT LCD Panels”).

SUMMARY OF THE INVENTION

A conventional example in Reference 2 is shown in FIGS. 37A and 37B(note that reference codes and the like have been changed). In a shiftregister circuit shown in FIGS. 37A and 37B, when an input signal isinputted to Vin, the electric potential of a terminal P1 rises and atransistor connected to a signal line V1 is turned ON. After that, thetransistor bootstraps in response to the rise of the electric potentialof the signal line V1, so electric potential of the signal line V1 istransmitted to the next stage without attenuation of the potential ofthe signal line V1. FIG. 37A shows a circuit diagram of the first fourstages of the shift register circuit, and so as to aid understanding ofthe circuit configuration, FIG. 37B shows the part of FIG. 37A which issurrounded by a broken line. FIG. 37B shows the minimum unit for formingthe circuit shown in FIG. 37A, and one circuit in FIG. 37B correspondsto one of the output terminals (OUT1 to OUT4) of the circuit in FIG.37A. In this specification, a structural unit of a circuit, such as thatshown in FIG. 37B with respect to FIG. 37A, is referred to as a singlestage circuit. Here, a transistor for controlling ON/OFF of theconnection between a terminal P1 and a power supply line Vss is turnedON in response to the output in the next stage; however, since the timewhile the transistor is ON is limited to the period during which theoutput of the next stage has a higher electric potential (H level), theterminal P1 and the terminal OUT1 are floated during most of the periodwhen a lower electric potential (L level) should be outputted to theterminal OUT1 (also referred to as a non-selection period). This alsoapplies to terminals Px and terminals OUTx in later stages. Accordingly,there has been a problem in that malfunction is caused due to noisegenerated by a clock signal 1 and a clock signal 2 or noise caused by anelectromagnetic wave from outside the circuit.

To counter these problems, in Reference 2, the configuration shown inFIGS. 38A and 38B is used. Note that FIG. 38A is a circuit diagram ofthe first six stages of a shift register circuit. So as to aidunderstanding of the circuit configuration, FIG. 38B shows the singlestage circuit of FIG. 38A which is surrounded by a broken line in FIG.38A. In the configuration illustrated in FIGS. 38A and 38B, a periodduring which a transistor that resets the terminal P1 and terminals Pxin later stages to an L level is ON, takes up most of a non-selectionperiod. With this configuration, in the non-selection period, variationin electric potential of the terminal P1 and the terminals Px in laterstages can be suppressed to some extent.

However, in the configurations shown in FIGS. 38A and 38B, in thenon-selection period, the terminal OUT1 and terminals OUTx in thefollowing stages are floated. Therefore, there is a problem in that aterminal OUT malfunctions due to noise generated by the clock signal 1and the clock signal 2, or noise caused by an electromagnetic wave fromoutside the circuit. Further, since a capacitor element is providedbetween an electrode connected to a gate electrode of the transistor forresetting terminals Px in each stage and the input terminal Vin in theconfiguration shown in FIGS. 38A and 38B; a load for driving the inputterminal Vin is heavy. Therefore, there are also the problems ofdistortion of waveforms of signals and heavy power consumption. Sincethe transistor for resetting the terminals Px in each stage is ON duringmost of the non-selection period, there is also a problem in thatvoltage stress is heavily biased on the gate electrode andcharacteristics vary easily.

In view of the above problems, it is an object of the present inventionto provide a semiconductor device which operates stably with fewmalfunctions due to noise, low power consumption, and little variationin characteristics; a display device including the semiconductor device;and an electronic device including the display device.

In the present invention, the term ‘display panel’ includes a liquidcrystal display panel constructed using a liquid crystal element, and adisplay panel having a light emitting element typified by anelectroluminescent (EL) element. Further, the display device includes adisplay device having the display panel and a peripheral circuit fordriving the display panel.

A semiconductor device in accordance with a mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, and a fourth terminal; afirst transistor for transmitting electric potential of the firstterminal to the output terminal; a rectifying element which turns ON thefirst transistor in accordance with electric potential of the inputterminal; a second transistor which fixes electric potential of theoutput terminal by conducting electricity the output terminal and thesecond terminal in accordance with electric potential of the fourthterminal; and a third transistor which fixes electric potential of thethird terminal by conducting electricity the third terminal and thesecond terminal in accordance with the electric potential of the fourthterminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, and afifth terminal; a first transistor for transmitting electric potentialof the first terminal to the output terminal; a rectifying element whichturns ON the first transistor in accordance with electric potential ofthe input terminal; a second transistor which fixes electric potentialof the output terminal by conducting electricity the output terminal andthe second terminal in accordance with electric potential of the fifthterminal; a third transistor which fixes electric potential of the thirdterminal by conducting electricity g the third terminal and the secondterminal in accordance with electric potential of the fourth terminal;and a circuit which reverses the electric potential of the thirdterminal and outputs the electrical potential to the fifth terminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, afifth terminal, and a sixth terminal; a first transistor fortransmitting electric potential of the first terminal to the outputterminal; a first rectifying element which turns ON the first transistorin accordance with electric potential of the input terminal; a secondtransistor which fixes electric potential of the output terminal byconducting electricity the output terminal and the second terminal inaccordance with electric potential of the fourth terminal; a thirdtransistor which fixes electric potential of the third terminal byconducting electricity the third terminal and the second terminal inaccordance with the electric potential of the fourth terminal; a secondrectifying element for increasing electric potential of the fifthterminal in accordance with the electric potential of the outputterminal; and a fourth transistor for connecting lowering electricpotential of the sixth terminal by conducting electricity the secondterminal the third terminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, afifth terminal, a sixth terminal, and a seventh terminal; a firsttransistor for transmitting electric potential of the first terminal tothe output terminal; a first rectifying element which turns ON the firsttransistor in accordance with electric potential of the input terminal;a second transistor which fixes electric potential of the outputterminal by conducting electricity the output terminal and the secondterminal in accordance with electric potentials of the seventh terminal;a third transistor which fixes electric potential of the third terminalby conducting electricity the third terminal and the second terminal inaccordance with the electric potential of the fourth terminal; a secondrectifying element for increasing electric potential of the fifthterminal in accordance with the electric potential of the outputterminal; a fourth transistor for connecting lowering electric potentialof the sixth terminal by conducting electricity the second terminal thethird terminal; and a circuit which reverses the electric potential ofthe third terminal and outputs the electrical potential to the seventhterminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, arectifying element, a first transistor, a second transistor, and a thirdtransistor. One of electrodes of the rectifying element is electricallyconnected to the input terminal, and the other electrode of therectifying element is electrically connected to the third terminal; agate electrode of the first transistor is electrically connected to thethird terminal, one of a source electrode and a drain electrode of thefirst transistor is electrically connected to the first terminal, andthe other of the source electrode and the drain electrode of the firsttransistor is electrically connected to the output terminal, a gateelectrode of the second transistor is electrically connected to thefourth terminal, one of a source electrode and a drain electrode of thesecond transistor is electrically connected to the second terminal, andthe other of the source electrode and the drain electrode of the secondtransistor is electrically connected to the output terminal; and a gateelectrode of the third transistor is electrically connected to thefourth terminal, one of a source electrode and a drain electrode of thethird transistor is electrically connected to the second terminal, andthe other of the source electrode and the drain electrode of the thirdtransistor is electrically connected to the third terminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, afifth terminal, a rectifying element, a first transistor, a secondtransistor, a third transistor, and a potential reversing circuit. Oneof electrodes of the rectifying element is electrically connected to theinput terminal, and the other electrode of the rectifying element iselectrically connected to the third terminal; a gate electrode of thefirst transistor is electrically connected to the third terminal, one ofa source electrode and a drain electrode of the first transistor iselectrically connected to the first terminal, and the other of thesource electrode and the drain electrode of the first transistor iselectrically connected to the output terminal; a gate electrode of thesecond transistor is electrically connected to the fifth terminal, oneof a source electrode and a drain electrode of the second transistor iselectrically connected to the second terminal, and the other of thesource electrode and the drain electrode of the second transistor iselectrically connected to the output terminal; a gate electrode of thethird transistor is electrically connected to the fourth terminal, oneof a source electrode and a drain electrode of the third transistor iselectrically connected to the second terminal, and the other of thesource electrode and the drain electrode of the third transistor iselectrically connected to the third terminal; and one of electrodes ofthe potential reversing circuit is electrically connected to the thirdterminal, the other electrode of the potential reversing circuit iselectrically connected to the fifth terminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, afifth terminal, a sixth terminal, a first rectifying element, a secondrectifying element, a first transistor, a second transistor, a thirdtransistor, and a fourth transistor. One of electrodes of the firstrectifying element is electrically connected to the input terminal, andthe other electrode of the first rectifying element is electricallyconnected to the third terminal; a gate electrode of the firsttransistor is electrically connected to the third terminal, one of asource electrode and a drain electrode of the first transistor iselectrically connected to the first terminal, and the other of thesource electrode and the drain electrode of the first transistor iselectrically connected to the output terminal; a gate electrode of thesecond transistor is electrically connected to the fourth terminal, oneof a source electrode and a drain electrode of the second transistor iselectrically connected to the second terminal, and the other of thesource electrode and the drain electrode of the second transistor iselectrically connected to the output terminal; a gate electrode of thethird transistor is electrically connected to the fourth terminal, oneof a source electrode and a drain electrode of the third transistor iselectrically connected to the second terminal, and the other of thesource electrode and the drain electrode of the third transistor iselectrically connected to the third terminal; one of electrodes of thesecond rectifying element is electrically connected to the outputterminal, and the other electrode of the second rectifying element iselectrically connected to the fifth terminal; and a gate electrode ofthe fourth transistor is electrically connected to the third terminal,one of a source electrode and a drain electrode of the fourth transistoris electrically connected to the second terminal, and the other of thesource electrode and the drain electrode of the fourth transistor iselectrically connected to the sixth terminal.

A semiconductor device in accordance with another mode of the presentinvention includes an input terminal, an output terminal, a firstterminal, a second terminal, a third terminal, a fourth terminal, afifth terminal, a sixth terminal, a seventh terminal, a first rectifyingelement, a second rectifying element, a first transistor, a secondtransistor, a third transistor, a fourth transistor, and a potentialreversing circuit. One of electrodes of the first rectifying element iselectrically connected to the input terminal, and the other electrode ofthe first rectifying element is electrically connected to the thirdterminal; a gate electrode of the first transistor is electricallyconnected to the third terminal, one of a source electrode and a drainelectrode of the first transistor is electrically connected to the firstterminal, and the other of the source electrode and the drain electrodeof the first transistor is electrically connected to the outputterminal; a gate electrode of the second transistor is electricallyconnected to the seventh terminal, one of a source electrode and a drainelectrode of the second transistor is electrically connected to thesecond terminal, and the other of the source electrode and the drainelectrode of the second transistor is electrically connected to theoutput terminal; a gate electrode of the third transistor iselectrically connected to the fourth terminal, one of a source electrodeand a drain electrode of the third transistor is electrically connectedto the second terminal, and the other of the source electrode and thedrain electrode of the third transistor is electrically connected to thethird terminal; one of electrodes of the second rectifying element iselectrically connected to the output terminal, and the other electrodeof the second rectifying element is electrically connected to the fifthterminal; a gate electrode of the fourth transistor is electricallyconnected to the third terminal, one of a source electrode and a drainelectrode of the fourth transistor is electrically connected to thesecond terminal, and the other of the source electrode and the drainelectrode of the fourth transistor is electrically connected to thesixth terminal; and one of electrodes of the potential reversing circuitis electrically connected to the third terminal, the other electrode ofthe potential reversing circuit is electrically connected to the seventhterminal.

With the structure of the present invention described above, a shiftregister circuit which operates stably with little malfunction due tonoise can be provided.

Further, in a semiconductor device in accordance with the presentinvention, the rectifying element may be a diode-connected transistor.In this case, the number of kinds of elements fabricated on thesubstrate can be reduced; thus, a manufacturing process can besimplified.

Further, a semiconductor device in accordance with the present inventionmay have a signal line which can turn ON the third transistor and thesecond transistor. In this case, a shift register circuit of whichoperation can be stopped at arbitrary timing and can be initialized canbe provided.

Further, a semiconductor device in accordance with the present inventionmay have a signal line which can reverse bias the third transistor andthe second transistor. In this case, a shift register circuit whichoperates stably with less characteristic variation can be provided.

Further, in a semiconductor device in accordance with the presentinvention, it is preferable that a signals inputted to the first clocksignal line and the second clock signal line each have a duty ratio ofless than 50%. Further, it is more preferable that a difference betweenthe middle of a period in which a signal inputted to one of them is atthe Low level and the middle of a period in which a signal inputted tothe other of them is at the High level may be in a range of 10% of theperiod of time of the clock signals. Thus, intervals between outputsignals outputted from respective output terminals, and highlysophisticated shift register circuit can be provided.

Further, in a semiconductor device in accordance with the presentinvention, it is preferable that the average of the area of the gateelectrode in the third transistor and the area of the gate electrode inthe second transistor is larger than the gate electrode in the firsttransistor. With this structure, electric potential of an outputterminal can be fixed stably, thereby providing a shift register circuitwith little malfunction due to noise.

Further, in a semiconductor device in accordance with the presentinvention, the power supply line, the first clock signal line, and thesecond clock signal line may be arranged on the opposite side of theoutput terminal with respect to the first transistor, the thirdtransistor, and the second transistor. With this structure, electricpotential of an output terminal can be fixed stably, thereby providing ashift register circuit with little malfunction due to noise.

Further, semiconductor device of the present invention comprises a firstwiring layer, a second wiring layer, a third wiring layer, an insulatingfilm, and an interlayer insulating film. The insulating film is formedbetween the first wiring layer and the second wiring layer. Theinterlayer insulating film is formed between the second wiring layer andthe third wiring layer. The interlayer insulating film is thicker thanthe insulating film. An electrode electrically connected to the firstelectrode is formed of at least the second wiring layer. An electrodeelectrically connected to the output terminal is formed of at least thefirst wiring layer and the third wiring layer. At a region where theelectrode electrically connected to the output terminal and theelectrode electrically connected to the first terminal are crossed, theelectrode electrically connected to the output terminal may be formed ofthe third wiring layer. With this structure, electric potential of anoutput terminal can be fixed stably, thereby providing a shift registercircuit with little malfunction due to noise.

Further, in a semiconductor device in accordance with the presentinvention, the shift register circuit is formed over the substrateprovided with the pixel area. With this structure, manufacturing cost ofthe display panel can be reduced.

Further, in another mode of a semiconductor device in accordance withthe present invention, the shift register circuit is provided as an ICover the substrate provided with the pixel area, and is connected to awiring on the substrate by COG (Chip On Glass). Thus, low powerconsumption display panel with little characteristic variation can beprovided.

Further, in another mode of a semiconductor device in accordance withthe present invention, the shift register circuit is provided as an ICover a connection wiring substrate connected to the substrate providedwith the pixel area, and connected to a wiring on the substrate by TAB(Tape Automated Bonding). Thus, low power consumption display panel withhigh reliability and little characteristic variation can be provided.

A semiconductor device in accordance with another mode of the presentinvention includes a first electrode, a second electrode, a thirdelectrode, a transistor, and a rectifying element. A gate electrode ofthe transistor is electrically connected to the second electrode, one ofa source electrode and a drain electrode of the transistor iselectrically connected to the first electrode, and the other of thesource electrode and the drain electrode of the transistor iselectrically connected to the third electrode; and one of electrodes ofthe rectifying element is electrically connected to the third electrode,the other electrode of the rectifying element is electrically connectedto the second electrode. Thus, a display panel which operates stablywith little characteristic variation can be provided.

A semiconductor device in accordance with another mode of the presentinvention includes a first electrode, a second electrode, a thirdelectrode, a fourth electrode, a first transistor, and a secondtransistor. A gate electrode of the first transistor is electricallyconnected to the second electrode, one of a source electrode and a drainelectrode of the first transistor is electrically connected to the firstelectrode, and the other of the source electrode and the drain electrodeof the first transistor is connected to the third electrode; and a gateelectrode of the second transistor is electrically connected to thefourth electrode, one of a source electrode and a drain electrode of thesecond transistor is electrically connected to the second electrode, andthe other of the source electrode and the drain electrode of the secondtransistor is electrically connected to the third electrode. Thus, adisplay panel which operates stably with little characteristic variationcan be provided.

Further, a display device in accordance with a mode of the presentinvention includes the above semiconductor device, an external drivercircuit, and a connection wiring substrate; a display panel and theexternal driver circuit are connected to each other with one connectionwiring substrate. Thus, a highly reliable display device with lessconnection points can be provided.

Further, a display device in accordance with another mode of the presentinvention includes the above semiconductor device, an external drivercircuit, and a plurality of connection wiring substrates; a displaypanel and the external driver circuit are connected to each other withconnection wiring substrate of a number of two or more and the number ofdivision of drivers (a data line driver and a source line driver) orless. Thus, since excellent performance is not required for the driver,even a large display panel with high reliability can be provided.

Further, an electronic device in accordance with the present inventionuses the display device as a display portion.

Note that the switch in this specification may be either an electricalswitch or a mechanical switch. Any type of switch may be used, as longas it can control the flow of current. A transistor, a diode (a PNdiode, a PIN diode, a Schottky diode, a diode-connected transistor, orthe like), or a logic circuit in which such diodes are combined may beused. Accordingly, when a transistor is used as a switch, the transistoris operated as simply a switch; therefore, there is no particularlimitation on the polarity (conductivity type) of the transistor.However, when low OFF current is desirable, a transistor having apolarity with less OFF current is preferably used. As the transistorwith less OFF current, a transistor having an LDD region, a transistorhaving a multigate structure, or the like can be used. Further, ann-channel transistor is preferably used when the electric potential of asource terminal of the transistor operating as a switch is close to thepotential of a lower potential power supply (Vss, GND, or 0 V), whereasa p-channel transistor is preferably used when the transistor operateswith the electric potential of the source terminal being close to thepotential of a higher potential power supply (Vdd or the like). Thishelps a transistor easily operate as a switch because the absolute valueof the gate-source voltage of the transistor can be increased. Note thata CMOS switch can also be applied, by using both n-channel and p-channeltransistors.

The display element is not limited, and for example, a display medium inwhich contrast is changed by electromagnetic force can be applied, suchas an EL element (an organic EL element, an inorganic EL element, or anEL element containing an organic material and an inorganic material), anelectron emissive element, a liquid crystal element, an electronic ink,a grating light valve (GLV), a plasma display (PDP), a digital micromirror device (DMD), a piezoelectric ceramic display, a carbon nanotube,or the like. Note that as display device using an EL element, an ELdisplay can be used; as a display device using an electron emissiveelement, a field emission display (FED), an SED flat panel display(Surface-conduction Electron-emitter Display), or the like can be used;as a display device using a liquid crystal element, a liquid crystaldisplay can be used; and as a display device using an electronic ink,electronic paper can be used.

There is no limit on the kind of transistor that can be applied to theinvention. Transistors which are applicable to the invention include athin film transistor (TFT) using a non-single crystalline semiconductorfilm typified by amorphous silicon and polycrystalline silicon, a MOStransistor which is formed using a semiconductor substrate or an SOIsubstrate, a junction transistor, a bipolar transistor, a transistorusing an organic semiconductor or a carbon nanotube, and other kinds oftransistors. There is no limit on the kind of substrate over which atransistor is provided, and a transistor can be provided over a singlecrystalline substrate, an SOI substrate, a glass substrate, or the like.

In the invention, “connected” means “electrically connected”. Therefore,in the structures disclosed by the invention, in addition to apredetermined connection, another element which makes electricalconnection possible (for example, another element (such as a transistor,a diode, a resistor, or a capacitor), a switch, or the like) may beprovided between given connected portions.

There is no particular limitation on the configuration of a transistor.For example, a multigate structure in which the number of gateelectrodes is two or more, a structure in which gate electrodes aredisposed above and below a channel, a structure in which a gateelectrode is disposed above a channel, a structure in which a gateelectrode is disposed below a channel, a staggered structure, or aninverted staggered structure may be used. Further, a channel region maybe divided into a plurality of regions, and the regions may be connectedin parallel or connected in series; a source electrode or a drainelectrode may overlap a channel (or a part of a channel); or an LDDregion may be provided.

Note that in this specification, a semiconductor device corresponds to adevice including a circuit having a semiconductor element (such as atransistor or a diode). In addition, a semiconductor device may be adevice in general which can operate utilizing semiconductorcharacteristics. Further, the term ‘display device’ may include not onlya main body of a display panel in which a plurality of pixels, includingdisplay elements such as a liquid crystal element or an EL element, anda peripheral driver circuit for driving the pixels are formed over asubstrate, but also a display panel provided with a flexible printedcircuit (FPC) or a printed wiring board (PWB). A light emitting devicerefers in particular to a display device using a self-light emittingdisplay element such as an element used in an EL element or an FED.

Further, among transistors in the present invention, a transistor inwhich a gate electrode is connected to either a source electrode or adrain electrode is occasionally referred to as a diode-connectedtransistor. All diode-connected transistors in the present invention canbe replaced with another rectifying element such as a PN junction diode,a PIN diode, or a light-emitting diode.

As described above, by utilizing the present invention, a semiconductordevice in which a terminal OUT is connected to a power supply line by asecond transistor during at least half of a period of time, whichoperates stably with few malfunctions due to noise; a display deviceincluding the semiconductor device; and an electronic device includingthe display device can be provided.

Further, when the average of the gate area of a third transistor and thegate area of a second transistor is made larger than the gate area of afirst transistor, since it is not necessary to connect a capacitorelement to an input terminal, load on the input terminal can beminimized. Thus, a semiconductor device with little waveform distortionand low power consumption; a display device including the semiconductordevice; and an electronic device including the display device can beprovided.

When a diode element or a diode-connected transistor is connected to agate electrode of a transistor which is ON for a long period, sufficientreverse bias can be applied to the gate electrode of the transistorwhich is ON for a long period. Thus, a semiconductor device whichoperates stably and has few variations in characteristics, a displaydevice including the semiconductor device, and an electronic deviceincluding the display device can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C illustrate a shift register circuit of the presentinvention and a timechart thereof.

FIGS. 2A to 2C illustrate shift register circuits of the presentinvention.

FIGS. 3A to 3C illustrate shift register circuits of the presentinvention.

FIG. 4 illustrates a timechart of a shift register circuit of thepresent invention.

FIGS. 5A to 5C illustrate shift register circuits of the presentinvention.

FIG. 6 illustrates a timechart of a shift register circuit of thepresent invention.

FIGS. 7A to 7C illustrate a shift register circuit of the presentinvention and a timechart thereof.

FIGS. 8A to 8C illustrate a shift register circuit of the presentinvention.

FIGS. 9A to 9D illustrate reverse bias circuits of the presentinvention.

FIGS. 10A to 10H illustrate reverse bias circuits of the presentinvention.

FIGS. 11A to 11C illustrate a shift register circuit of the presentinvention.

FIG. 12 illustrates a timechart of a shift register circuit of thepresent invention.

FIGS. 13A to 13C illustrate a shift register circuit of the presentinvention and a timechart thereof.

FIGS. 14A to 14C illustrate a shift register circuit of the presentinvention.

FIGS. 15A to 15D illustrate reverse bias-reset circuits of the presentinvention.

FIGS. 16A to 16H illustrate reverse bias-reset circuits of the presentinvention.

FIG. 17 is a top view of a shift register circuit of the presentinvention.

FIG. 18 is a cross-sectional view of a shift register circuit of thepresent invention.

FIG. 19 is a top view of a shift register circuit of the presentinvention.

FIG. 20 is a top view of a shift register circuit of the presentinvention.

FIG. 21 is a top view of a shift register circuit of the presentinvention.

FIGS. 22A and 22B are cross-sectional views of a shift register circuitapplied to the present invention.

FIG. 23 is a top view of a shift register circuit of the presentinvention.

FIGS. 24A and 24B are cross-sectional views of a shift register circuitapplied to the present invention.

FIG. 25 is a top view of a shift register circuit of the presentinvention.

FIG. 26 is a top view of a shift register circuit of the presentinvention.

FIGS. 27A and 27B are cross-sectional views of a shift register circuitof the present invention.

FIG. 28 is a top view of a shift register circuit of the presentinvention.

FIGS. 29A and 29B are cross-sectional views of a shift register circuitof the present invention.

FIG. 30 is a top view of a shift register circuit of the presentinvention.

FIGS. 31A to 31E illustrate display panels using shift register circuitsof the present invention.

FIG. 32 illustrates a display device using a shift register circuit ofthe present invention.

FIG. 33 illustrates a display device using a shift register circuit ofthe present invention.

FIGS. 34A to 34H illustrate electronic devices using shift registercircuits of the present invention.

FIGS. 35A to 35F illustrate operations of shift register circuits of thepresent invention.

FIGS. 36A to 36D illustrate shift register circuits of the presentinvention and timecharts thereof.

FIGS. 37A and 37B illustrate a conventional shift register.

FIGS. 38A and 38B illustrate a conventional shift register.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Modes

Embodiment Modes of the present invention will be described withreference to the drawings. Note that the present invention can beembodied with many different modes, and it is easily understood by thoseskilled in the art that the modes and details can be variously modifiedwithout departing from the spirit and scope of the present invention.Therefore, the present invention should not be construed as beinglimited to the description of the Embodiment Modes. In the structures ofthe invention described hereinafter, the same reference numerals aregiven to the same parts or parts having similar functions in differentdrawings, and the description of such parts will not be repeated.

Embodiment Mode 1

In this embodiment mode, a circuit configuration of a shift registerwhere the electric potential of an output terminal is fixed to anon-selection period, thereby reducing the occurrence of malfunctionsdue to clock signals or noise, will be described. Circuit configurationexamples of a shift register of the present invention are shown in FIGS.1A to 1C. FIG. 1A shows the entire circuit configuration of a shiftregister circuit of the present invention. FIG. 1B shows a configurationexample of a circuit 10 which shows a single stage circuit of a shiftregister of the present invention. Note that in this specification, asingle stage circuit refers to a minimum unit for forming a circuit,which corresponds to an output terminal (L(1) to L(n)) of the circuit,as does FIG. 1B with respect to FIG. 1A. FIG. 1C shows waveforms of aninput signal, an internal electrode, and an output signal in the circuitshown in FIGS. 1A and 1B.

The circuit shown in FIG. 1A is provided with a start pulse terminal SP,a first clock signal line CLK1 (also referred to as a first wiring), asecond clock signal line CLK2 (also referred to as a second wiring), apower supply line Vss, a transistor 18, n number of circuits 10 (where nis an integer greater than or equal to two), and an output terminal L(k)(where k is an integer of greater than or equal to one and less than orequal to n) provided corresponding to the circuits 10. In FIGS. 1A to 1C(and all corresponding diagrams in this specification), a kth stagewhere k is an integer greater than or equal to one and less than orequal to n is not shown; however, the output terminal L(k) is providedbetween an output terminal L(1) and an output terminal L(n), and aterminal P(k) is provided between a terminal P(1) and a terminal P(n).The circuit 10 shown in FIG. 1B is provided with a terminal IN, aterminal OUT, a terminal G, a terminal R, a terminal F, a terminal B, aterminal C, transistors 11, 12, 13, 15, 16, and 17, a capacitor element14, and a terminal P. Note that in this specification, a terminal is anelectrode in a circuit which electrically connected to the external.Here, the transistor 11 may be another element having rectifyingcharacteristics, and is used as a rectifying element for input (alsoreferred to as a first rectifying element). Further, the transistor 15may be another element having rectifying characteristics, and is used asa rectifying element for reset (also referred to as a second rectifyingelement). The transistor 12 is used as a transmission transistor (alsoreferred to as a first transistor). The transistor 13 is used as aninternal voltage clamp transistor (also referred to as a thirdtransistor). The transistor 17 is used as an output voltage clamptransistor (also referred to as a second transistor). The transistor 16is used as a set transistor (also referred to as fourth transistor).

Note that a terminal P of the circuit 10 at a kth stage is also referredto as a terminal P(k). Further, this embodiment mode specifies acapacitor element 14; however, functions of the capacitor element 14 canalso be realized by parasitic capacitance formed between a gateelectrode and a drain electrode (or a source electrode) of thetransistor 12. Therefore, the present invention includes not only thecase where the capacitor element 14 is formed as an independentelectrical element, but also the case where the capacitor element 14 isa parasitic capacitor element which is associated with the transistor12.

The gate electrode of transistor 11 of the circuit 10 shown in FIG. 1Bis connected to a terminal IN, one of a source electrode and a drainelectrode of the transistor 11 is connected to the terminal IN, and theother of the source electrode and the drain electrode of the transistor11 is connected to the terminal P. The gate electrode of the transistor12 is connected to the terminal P, one of the source electrode and thedrain electrode of the transistor 12 is connected to the terminal C, theother of the source electrode and the drain electrode of the transistor12 is connected to the terminal OUT.

Further, the gate electrode of the transistor 13 is connected to aterminal R, one of a source electrode and a drain electrode of thetransistor 13 is connected to a terminal G, and the other of the sourceelectrode and the drain electrode of the transistor 13 is connected tothe terminal P. Further, one of electrodes of the capacitor element 14is connected to the terminal P, the other of the electrodes of thecapacitor element 14 is connected to the terminal OUT.

The gate electrode of the transistor 15 is connected to a terminal OUT,one of a source electrode and a drain electrode of the transistor 15 isconnected to the terminal OUT, and the other of the source electrode andthe drain electrode of the transistor 15 is connected to a terminal B.Further, the gate electrode of the transistor 16 is connected to theterminal P, one of a source electrode and a drain electrode of thetransistor 16 is connected to a terminal G, and the other of the sourceelectrode and the drain electrode of the transistor 16 is connected to aterminal F. Further, the gate electrode of the transistor 17 isconnected to the terminal R, one of a source electrode and a drainelectrode of the transistor 17 is connected to the terminal G, and theother of the source electrode and the drain electrode of the transistor17 is connected to the terminal OUT.

As shown in FIG. 1A, the terminal IN of the circuit 10 at a first stageis connected to a start pulse terminal SP and the gate electrode of thetransistor 18. Further, an electrode SR(1) at a first stage is connectedto a terminal B of the circuit 10 at a second stage, and one of a sourceelectrode and a drain electrode of the transistor 18. The other of thesource electrode and the drain electrode of the transistor 18 isconnected to the power supply line Vss. Further, the power supply lineVss is connected to the terminal G at each stage of the circuit 10.Still further, the first clock signal line CLK1 connected to theterminal C at each of odd-numbered stages of the circuit 10, and thesecond clock signal line CLK2 is connected to the terminal C at each ofeven-numbered stages.

Next, connection of the circuit 10 at a kth stage in the circuit shownin FIG. 1A will be described. An electrode SR(k) connected to theterminal R of the circuit 10 at the kth stage is connected to theterminal B of the circuit 10 at a (k+1)th stage and the terminal F ofthe circuit 10 at a (k−1)th stage. Further, the output terminal L(k)connected to the terminal OUT of the circuit 10 at a kth stage isconnected to the terminal IN of the circuit 10 at a (k+1)th stage. Here,as shown in FIG. 1A, connection of the circuit 10 at either a firststage or an nth stage may be different from a connection of the circuit10 at the other stages. For example, an electrode SR(n) at the nth stagemay be connected to an electrode SR(n-1)

Here, in this embodiment mode, the number n of the circuit 10 is an oddnumber; however, in the present invention in, n may be an even number.Further, in this embodiment mode, the first clock signal line CLK1 isconnected to the terminal C of the circuit 10 at an odd-numbered stage,the second clock signal line CLK2 is connected to the terminal C of thecircuit 10 at an even-numbered stage. Alternatively, in the presentinvention, the connection of CLK1 and CLK2 may be reversed,specifically, the first clock signal line CLK1 may be connected to theterminal C of the circuit 10 at an even-numbered stage, and the secondclock signal line CLK2 may be connected to the terminal C of the circuit10 at an odd-numbered stage. Further, in the present invention, thenumber of clock signal lines is not limited to two, it may be two ormore. In such case, it is preferable that the number of kinds (number ofphase) of signals inputted to the click signal line is the same as thenumber of clock signal lines. For example, it is preferable that in acase using three clock signal lines, the number of kinds (three ofphase) of clock signals inputted to the circuit 10 is three.

Next, the operation of a circuit shown in FIGS. 1A and 1B will bedescribed with reference to FIG. 1C. FIG. 1C is a timing chartillustrating waveforms of signals inputted to the circuit shown in FIGS.1A and 1B, internal electrodes, and the output signals. The verticalaxis indicates electric potentials of the signals, the input signals andthe output signals may be digital signals having either electricpotential of a high level (also referred to as an H level or a Vddlevel) or a low level (also referred to as an L level or a Vss level).The horizontal axis indicates time. In this embodiment mode, descriptionis given of input signals are inputted repeatedly based on the time T0.Note that the present invention is not limited thereto, and includes thecase where the input signals may be variously changed to obtain adesired output signal.

Further, in this embodiment mode, an operation of selecting (scanning)output terminal L(1) to OUT(n) are sequentially selected as outputsignals (scan) will be described. This operation is widely applied to,for example, in an active matrix display device, a peripheral driverwhich controls ON/OFF of switches for selecting pixels. Note that, inthis embodiment mode, signals inputted to the start pulse terminal SP,the first clock signal line CLK1, and the second clock signal line CLK2in FIG. 1C are collectively referred to as an input signal. Further, theelectric potential of the power supply line Vss is assumed to be almostequal to the electric potential of the L level of the input signal.However, electric potential of the power supply line Vss in the presentinvention is not limited thereto.

Next, an operation of the circuit shown in FIGS. 1A to 1C will bedescribed as in summary with reference to FIGS. 35A to 35F. FIGS. 35A to35F illustrate operation of a circuit in FIG. 1B in chronological order.The transistors indicated in broken lines in FIGS. 35A to 35F are in anOFF-state, and transistors indicated in continuous lines are in anON-state. Further, the arrows in the diagrams indicate directions ofcurrent in operations at the points. Further, electric potentials of anelectrode and a terminal in the diagrams at that point are enclosed in< >. Note that, electric potential of a clock signal is represented as<Vss> assuming that the lower electric potential is the electricpotential of the power supply line Vss, or as <Vdd> which is the higherelectric potential.

First, referring to FIG. 35A, an operation of canceling a resetoperation of a current stage by a preceding stage will be explained.Here, in this specification, an operation of increasing the electricpotential of the terminal R to turn ON the internal voltage clamptransistor 13 and the output voltage clamp transistor 17 is referred toas a reset operation. On the other hand, an operation of decreasing theelectric potential of the terminal R to turn OFF the internal voltageclamp transistor 13 and the output voltage clamp transistor 17 isreferred to as a set operation. During reset operation, electricpotentials of the terminal P and the terminal OUT are forced to be<Vss>. Therefore, in order to operate the circuit 10, set operation isrequired first. The set operation may be conducted by making thepotential of the terminal R of the stage be <Vss> using the settransistor 16 of the preceding stage at a time where the electricpotential of the terminal P of the preceding stage increases. In FIG.35A, the transistors 11, 12, 13, 15, 16, and 17 are all in an OFF-state,which may be considered as an initialized state.

Next, referring to FIG. 35B, pulse input operation will be described. Apulse is inputted to the terminal IN, and then, electric potential ofthe terminal IN increases. The electric potential of the terminal INrises above the electric potential of the terminal P by the thresholdvoltage of the transistor 11 (also referred to as Vth11) or more, andthus, the transistor 11 is turned ON. Accordingly, electric potential ofthe terminal P also rises to be <Vdd-|Vth11|> which is lower than theelectric potential of the terminal IN <Vdd> by Vth11. The transistors 11and 16 are turned ON, then, the potential of the terminal OUT becomesequal to the electric potential <Vss> of the terminal C. Further,electric potential of the terminal F becomes <Vss>; thus, electricpotential of the terminal R of the following stage will be <Vss>. Thatis, the following stage is subjected to set operation by the settransistor 16 of the current stage.

Next, referring to FIG. 35C, bootstrap operation will be described. Theterminal IN which has increased the electric potential of the terminal Pmay be returned to the electric potential <Vss> at arbitrary timing. Thetransistor 11 is diode connected and is in an OFF-state even when theelectric potential of the terminal IN returns to <Vss>. Therefore, thetransistor 11 does not affect the electric potential of the terminal P.That is, the transistor 11 increases the electric potential of theterminal P in accordance with the increase in the electric potential ofthe terminal IN, but is not required to lower it, and is used as arectifying element for input.

In the case where the electric potential of the terminal P hasincreased, a clock signal is inputted and the electric potential of theterminal C becomes <Vdd>, current flows through the transmissiontransistor 12 from the terminal C toward the terminal OUT, and theelectric potential of the terminal OUT also increases. At that time,since the terminal P and the terminal OUT are connected by the capacitorelement 14, the electric potential of the terminal P also increases inaccordance with the increase in the electric potential of the terminalOUT. The value to which the electric potential of the terminal Pincreases depends on the capacitance value of parasitic capacitorelements other than the capacitor element 14 connected to the terminalP. As long as the electric potential is <Vdd+|Vth11|> or more, there isproblem with operation, and the electric potential of the terminal OUTincreases to <Vdd>, equal to the potential of the clock signal.Accordingly, in the diagram, the electric potential of the terminal P atthat time is represented as <Vdd+|Vth11|(upward arrow)>, meaning anelectric potential of <Vdd+|Vth11|> or more.

Next, referring to FIG. 35D, an operation of resetting the precedingstage by the current stage will be described. As shown in FIG. 35C, whenthe electric potential of the terminal OUT is increased to <Vdd>, thetransistor 15 is turned ON, and the electric potential of the terminal Bincreases accordingly. Since the transistor 15 turns OFF when theelectric potential of the terminal B decreases from the electricpotential of the terminal OUT by the threshold voltage of the transistor15 (also referred to as Vth15), the increase of the electric potentialof the terminal B stops, and the electric potential of the terminal B is<Vdd-|Vth15|>. Hereupon, since the electric potential of the terminal Rof the preceding stage increases to <Vdd-|Vth15|>, the preceding stageis reset, and the electric potential of the terminal P and the terminalOUT of the preceding stage is fixed at <Vss>; thus, a pulse is notinputted to the terminal IN of the current stage.

Next, referring to FIG. 35E, an operation of a clock signal returning toVss will be described. When the electric potential of the clock signalreturns to <Vss>, and the electric potential of the terminal C returnsto <Vss>, the transmission transistor 12 is in an ON-state. Therefore,current flows through the transmission transistor 12 from the terminalOUT toward the terminal C; thus, the electric potential of the terminalOUT also returns to <Vss>. Thereupon, the electric potential of theterminal P also returns to <Vdd-|Vth11|>. Further, since the transistor15 is in an OFF-state, the electric potential of the terminal B remainsat <Vdd-|Vth15|> even when the electric potential of the terminal OUTreturns to <Vss>. In other words, the transistor 15 increases electricpotential of the terminal B in accordance with the electric potential ofthe terminal OUT but is not required to lower it, and is used as arectifying element for reset.

Next, referring to FIG. 35F, an operation of resetting the current stageby the next stage will be described. When an increase in the electricpotential of the terminal OUT of the current stage is transmitted to theterminal IN of the next stage, the electric potential of the terminalOUT of the next stage increases, and the transistor 15 of the next stageturns ON. Thereby the electric potential of the terminal B of the nextstage increases, and the electric potential of the terminal R of thecurrent stage increases to <Vdd-|Vth15|>. Accordingly, the current stageis reset. Thereupon, the internal voltage clamp transistor 13 and theoutput voltage clamp transistor 17 of the current stage is turned ON,and the terminal P and the terminal OUT are each fixed at an electricpotential of <Vss>. Thus, the current stage is reset by the operation ofthe next stage, and thereby the transmission transistor 12 is turnedOFF. Accordingly, electrical continuity between the terminal OUT and theterminal C is interrupted.

This interruption ends when the electric potential of the terminal R islowered due to leakage current of an element connected to the terminalR, and the internal voltage clamp transistor 13 and the output voltageclamp transistor 17 are naturally turned OFF accordingly, or when theset transistor 16 of the preceding stage is turned ON and the electricpotential of the terminal R becomes <Vss> accordingly, so that theinternal voltage clamp transistor 13 and the output voltage clamptransistor 17 are forcedly turned OFF (See FIG. 35A). The period fromthe state shown in FIG. 35F to the state shown in FIG. 35A is referredto as a non-selection period in this specification. It is important tostabilize and fix the electric potentials of the terminal P and theterminal OUT to <Vss> in the non-selection period. In other words, it isimportant to maintain the ON-state of a transistor with its gateelectrode connected to the terminal R.

Note that a single stage circuit in a shift register circuit of thepresent invention includes an output voltage clamp transistor, so thatthe output terminal is prevented from being floated when thetransmission transistor is in an OFF-state, thereby establishingelectrical continuity with the power supply line. Therefore, how thereset operation or the set operation of the terminal R is conducted isnot limited to the above example. The configurations shown in FIGS. 36Aand 36C may be used for the single stage circuit.

A circuit 310 shown in FIG. 36A includes terminals IN, OUT, R, G, and C,a terminal P, and transistors 311, 312, 313, and 317. The gate electrodeof the transistor 311 is connected to the terminal IN, one of a sourceelectrode and a drain electrode of the transistor 311 is connected tothe terminal IN, the other of the source electrode and the drainelectrode of the transistor 311 is connected to the terminal P. The gateelectrode of the transistor 312 is connected to the terminal P, one of asource electrode and a drain electrode of the transistor 312 isconnected to the terminal C, and the other of the source 20 electrodeand the drain electrode of the transistor 312 is connected to theterminal OUT.

The gate electrode of the transistor 313 is connected the terminal R,one of a source electrode and a drain electrode of the transistor 313 isconnected to the terminal and the other of the source electrode and thedrain electrode of the transistor 313 is connected to the terminal P.The gate electrode of the transistor 317 is connected to the terminal R,one of a source electrode and a drain electrode of the transistor 317 isconnected to the terminal Q and the other of the source electrode andthe drain electrode of the transistor 317 is connected to the terminalOUT. Note that the transistor 311 may be used as a rectifying elementfor input (a first rectifying element).

Further, the transistor 312 may be used as a transmission transistor (afirst transistor). The transistor 317 may be used as an output voltageclamp transistor (a second transistor). The transistor 313 may be usedas an internal voltage clamp transistor (a third transistor).

Here, an operation of the circuit shown in FIG. 36A will be describedwith reference to FIG. 36B. FIG. 36B is a timing chart of the change inelectric potential of each terminal shown in FIG. 36A. Description willbe given of the case where a clock signal is inputted to the terminal C,a pulse for increasing the electric potential of the terminal P isinputted to the terminal IN, the terminal G is fixed to the L level, anda pulse for lowering the electric potential of the terminal P isinputted to the terminal R.

When the electric potential of the terminal R is low, and a pulse isinputted to the terminal IN with the internal voltage clamp transistorand the output voltage clamp transistor in an ON-state, the electricpotential of the terminal P is increased through the rectifying elementfor input, so the transmission transistor is turned ON. After that, whenthe electric potential of the terminal C is increased, the transmissiontransistor bootstraps, and the electric potential of the terminal C istransmitted to the terminal OUT as is. After that, when the electricpotential of the terminal R increases, the internal voltage clamptransistor and the output voltage clamp transistor are turned ON, so theterminal P and the terminal OUT are fixed to the L level. However, asignal waveform of a signal inputted to the circuit 310 of the presentinvention is not limited to these.

In this manner, in the circuit 310 of the present invention, a signalinputted to the terminal C can be transmitted to the terminal OUT onlyduring a period in which the electric potential of the terminal R islow. Further, in a period during which the electric potential of theterminal R is high, the terminal P and the terminal OUT can be fixed tothe L level.

A circuit 320 shown in FIG. 36C includes terminals IN, OUT, R, G, and C,15 terminals P and Q, and transistors 321, 322, 323, and 327 a, aninverter 327 b, and the capacitor element 324. Note that the capacitorelement 324 is not necessarily connected as in FIG. 36A. The gateelectrode of the transistor 321 is connected to the terminal IN, one ofa source electrode and a drain electrode of the transistor 321 isconnected to the terminal IN, and the other of the source electrode andthe drain electrode of the transistor 321 is connected to the terminalP.

The gate electrode of the transistor 322 is connected to the terminal P,one of a source electrode and a drain electrode of the transistor 322 isconnected to the terminal C, and the other of the source electrode andthe drain electrode of the transistor 322 is connected to the terminalOUT. The gate electrode of the transistor 323 is connected to theterminal R, one of a source electrode and a drain electrode of thetransistor 323 is connected to the terminal G and the other of thesource electrode and the drain electrode of the transistor 327 isconnected to the terminal P. One of electrodes of the capacitor element324 is connected to the terminal P, and the other electrode of thecapacitor element 324 is connected to the terminal OUT. The gateelectrode of the transistor 327 a is connected to the terminal Q, one ofa source electrode and a drain electrode of the transistor 327 a isconnected to the terminal G, and the other of the source electrode andthe drain electrode of the transistor 327 a is connected to the terminalOUT.

An input electrode of the inverter 327 b is connected to the terminal P,and an output electrode of the inverter 327 b is connected to theterminal Q. Note that the transistor 321 may be used as a rectifyingelement for input (a first rectifying element). Further, the transistor322 may be used as a transmission transistor (a first transistor). Stillfurther, the transistor 327 a may be used as an output voltage clamptransistor (a second transistor). Moreover, the transistor 323 may beused as an internal voltage clamp transistor (a third transistor).

Here, an operation of the circuit shown in FIG. 36C will be explainedwith reference to FIG. 36D. FIG. 36D is a timing chart of change inelectric potential of each terminal shown in FIG. 36C. Description willbe given of the case where A clock signal is inputted to the terminal C,a pulse for increasing the electric potential of the terminal P isinputted to the terminal IN, the terminal G is fixed to the L level, anda pulse for lowering the electric potential of the terminal P isinputted to the terminal R.

When the electric potential of the terminal R is low, and the internalvoltage clamp transistor is in an OFF-state, if a pulse is inputted tothe terminal IN, the electric potential of the terminal P is increasedthrough the rectifying element for input, and thereby the transmissiontransistor is turned ON. At that time, since the electric potential ofthe terminal P is reversed, the terminal Q changes to L level.Therefore, the output voltage clamp transistor is in an OFF-state. Afterthat, when the electric potential of the terminal C is increased, thetransmission transistor bootstraps, and the electric potential of theterminal C is transmitted to the terminal OUT as is. Further, when theelectric potential of the terminal R is increased, the internal voltageclamp transistor is turned ON; thus, the terminal P is fixed to the Llevel. Accordingly, the electric potential of the terminal Q becomes theH level, and thus, the output voltage clamp transistor is turned ON, andthe terminal OUT is fixed to the L level. In this manner, in the circuit320 of the present invention, a signal inputted to the terminal C can betransmitted to the terminal OUT only during a period in which theelectric potential of the terminal R is low. Further, during a period inwhich the electric potential of the terminal R is high, the terminal Pand the terminal OUT can be fixed to the L level. However, a signalwaveform of a signal inputted to the circuit 320 of the presentinvention is not limited to these.

Next, with reference to FIGS. 1A to 1C, start pulse which is to beinputted to a start pulse terminal SP at a time of T0 will be described.The pulse width of the start pulse is arbitrary. Assuming that the aperiod of a signal inputted to the first clock signal line CLK1 and thesecond clock signal line CLK2 is Tc, the pulse width is preferably Tc/2or more and Tc or less. Thus, the electric potential of a terminal P(1)which is connected to the start pulse terminal SP through thediode-connected transistor 11 can be increased sufficiently. Further,when the electric potential of the terminal P is lowered due to anON-state of the transistor 13 of the circuit 10, power consumption canbe suppressed because there is no path of stationary current through theterminal IN, the transistor 11, the terminal P, the transistor 13, andthe terminal G sequentially, which is preferable.

Next, a signal to be inputted to the first clock signal line CLK1 andthe second clock signal line CLK2 will be described. It is preferablethat the percentage of a first clock signal and a second clock signal atH level in one period of time (duty ratio) is less than 50%. Further, itis more preferable that a difference between the middle of a period inwhich one of the signals is at H level and the middle of a period inwhich the other signal is at L level is within a range of 10% of theperiod of time. Thus, an output signal can be similar to a pulse signalhaving a single frequency. Further, the H levels of adjacent outputterminals are prevented from temporally overlapping. This isadvantageous since a plurality of rows can be prevented from beingselected simultaneously when using a shift register circuit as aperipheral driver circuit for controlling ON/OFF of a switch forselecting pixels in an active matrix display device in this embodimentmode.

Description will be given of change in the potential of the terminalP(1) when a start pulse is inputted at a time of T0 at the initialpotential of the terminal P(1) in the circuit 10 of the first stage isat the L level and the potential of the terminal IN changes from the Llevel to the H level. Here, the terminal R is at L level, and thetransistor 13 is in an OFF-state. Accordingly, the transistor 11 isturned ON, and the electric potential of the terminal P(1) increases.Then, when the electric potential of the terminal P(1) increases to apotential of the H level of the start pulse minus the threshold voltageof the transistor 11, the transistor 11 is turned OFF. Thus, increase inthe electric potential of the terminal P(1) stops. When the electricpotential of the terminal P(1) once increases, even if the electricpotential of the terminal IN drops and returns to the L level afterthat, the transistor 11 remains OFF. Therefore, the electric potentialof the terminal P(1) is not reduced and is floated.

Hereupon, in a state where the electric potential of the terminal P(1)is increased, since the electric potential of the terminal C is the Llevel, the transistor 12 is turned ON. Accordingly, the L level ifoutputted to the terminal OUT. After that, the electric potential of theterminal C increases, the electric potential of the terminal OUT is alsoincreased. Further, since the terminal P(1) is floated, the electricpotential of the terminal P(1) also increases as the electric potentialof the terminal OUT increases through the capacitor element 14. Thus,due to the bootstrap operation by the transistor 12, change in theelectric potential of the terminal C is transmitted to the terminal OUTwithout attenuation.

In this manner, during a period in which the transistor 13 is in anOFF-state and the terminal P(1) is floated still with a high electricpotential, and change of the electric potential of the terminal C istransmitted to the terminal OUT as it is. Therefore, in the case where aclock signal is not outputted to the output terminal as it is, thetransistor 13 is turned ON at a certain time by increasing the electricpotential of the terminal R; thus, the electric potential of theterminal P(1) becomes the L level. Then, the transistor 12 is turnedOFF, thereby the electric potential of the terminal C is not transmittedto the terminal OUT as it is.

The terminal OUT is connected to the terminal IN of the circuit 10 ofthe second stage through the output terminal L(1). Specifically, theoutput of the circuit 10 at the first stage functions as a start pulse;thus, the circuit 10 at the second stage operates in the same manner asthe above-described circuit 10 of the first stage.

Next, the timing of reset operation will be described. The timing ofperforming the reset operation is arbitrary; reset operation may beconducted at a point where one pulse of a clock signal is transmittedfrom the terminal C to the terminal OUT. Specifically, reset operationof a kth stage may be conducted at the time where the electric potentialof the terminal OUT of (k+1)th stage rises. Further, as a circuitconfiguration of this case, as shown in FIGS. 1A and 1B, it ispreferable to use a configuration in which the terminal OUT and theterminal B of the (k+1)th stage is connected through the diode-connectedtransistor 15, and the terminal B of the (k+1)th stage is connected tothe terminal R of the kth stage using the electrode SR(k).

When using this configuration, a clock signal is transmitted to theterminal OUT of the circuit 10 at the kth stage, and when the clocksignal is inputted to the terminal IN of the circuit 10 at the (k+1)thstage, a clock signal having a phase different from the output signal ofthe circuit 10 at the kth stage is outputted to the terminal OUT of thecircuit 10 at the (k+1)th stage. Hereupon, the electric potential of theterminal B of the circuit 10 at the (k+1)th stage rises with the sametiming as when the electric potential of the terminal OUT of the circuit10 at the (k+1)th stage rises. Specifically, the electric potential ofthe terminal R in the circuit 10 at the kth stage rises with the sametiming as when the electric potential of the terminal OUT in the circuit10 at the (k+1)th stage rises, thereby the circuit 10 of the kth stageis reset. When the electric potential of the terminal OUT in the circuit10 at the (k+1)th stage rises, since the circuit 10 at the kth stageoutput the L level after transmitting a pulse of the clock signal, thepulse of the output terminal is one. In this manner, an output terminalof the shift register of this embodiment mode is at H level sequentiallyform an OUT(1); therefore, the shift register can be used for aperipheral driver circuit for controlling ON/OFF of a switch forselecting pixels in an active matrix display device.

Note that, the timing of reset operation of the present invention is notlimited thereto and the reset operation can be conduced at any timing.For example, reset operation may be conduced when the electric potentialof the output terminal of a stage two stages after the current stagerises, or when the electric potential of output terminal of a stage morethan three stages after the current stage rises. At that time, as thesignal line which defines the timing for reset operation is distant fromthe current stage, the distance of leading the electrode SR becomeslonger, so that the value of parasitic capacitance associated with theelectrode SR becomes larger. That is advantageous for maintaining theelectric potential of the electrode SR.

Reset operation of the last stage may be conduced by output of the laststage itself by connecting the electrode SR(n) and an electrode SR(n−1)as shown in FIG. 1A. Thus, reset (operation of return to the electricpotential of the power supply line Vss) of the terminal P(n) and theoutput terminal L(n) can be conducted. Further, a common timing pulsemay be additionally inputted to all the stages for the reset operation.Alternatively, the start pulse may be used as a common timing pulse.

Next, a period other than the period in which the output terminal L(k)of the kth stage is conducting to the clock signal line through thetransistor 12 in an ON-state (a period in which the electric potentialof the terminal P(k) is at L level in FIG. 1C). In the (k+1)th stage ofthe circuit 10, when the electric potential of the terminal OUT rises,since the diode-connected transistor 15 is in an ON-state, the electricpotential of the terminal B increases to a potential of the H levelminus the threshold voltage transistor 15. However, when the electricpotential of the terminal OUT drops, the transistor 15 is turned OFF;thus, the electric potential of the terminal B does not drop. Thus, theelectric potential of the electrode SR(k) rises due to the electricpotential of the terminal OUT of the (k+1)th stage rises but does notdrop. Therefore, the electric potential of the terminal R of after resetoperation of the kth stage is held at H level, and the transistors 13and 17 remain ON accordingly. Thus, the electric potential of theterminal P(k) and the electric potential of the terminal OUT are fixedat L level.

If the electric potential of the terminal R reset after the resetoperation is not held at H level, the transistors 13 and 17 is turnedOFF; therefore, the terminal P(k) and the terminal OUT would be floated.Since the terminal P(k) is connected to one of the first clock signalline and the second clock signal line through the gate capacitor of thetransistor 12, if the terminal P(k) is floated, the electric potentialof the terminal P(k) is varied easily. Further, since the terminal OUTis capacitively coupled with the terminal P(k) through capacitor element14, if the electric potential of the terminal P(k) is varied when theterminal OUT is floated, the electric potential of the terminal OUT isalso varied. In addition, the electric potential of the output terminalL(k) is varied even by parasitic capacitance with the clock signal line.The variation in the electric potential of the output terminal L(k)cause instability of the shift register circuit and malfunctions;therefore, it is very important to hold the electric potential of theterminal R at H level in order to fix the electric potentials of theterminal P and the terminal OUT.

Note that, it is preferable that a period during which the electricpotential of the terminal R is held at H level for fixing the electricpotentials of the terminal P and the terminal OUT be at least half of aperiod of a start pulse.

Note that since the electric potentials of the electrode SR and theterminal R are held at H level after reset operation, the capacitorelement is not required to be connected. The average of the areas of thegate electrode of the internal voltage clamp transistor 13 and theoutput voltage clamp transistor 17 is larger than the area of thetransmission transistor 12; thus, the electric potentials of theelectrode SR ad the terminal R can be held at H level after the resetoperation. Further, the length of leading the electrode SR from theterminal R at the kth stage is longer than a pitch between the circuit10 of the kth stage and the circuit 10 of the (k+1)th stage, so that thevalue of the parasitic capacitance associated with the electrode SR isincreased, thereby holding the electric potentials of the electrode SRand the terminal R. Naturally, the electric potentials of the electrodeSR and the terminal R may be held by connecting a capacitor elementbetween the electrode SR and the power supply line Vss or the startpulse terminal SP.

As mentioned above, it is very important to hold the electric potentialsof the terminal R and the electrode SR at H level after reset operationfor stable operation of the shift register circuit. However, in the casewhere after the shift register circuit is operated once, a start pulseis inputted again, and then the circuit 10 at the kth stage is notoperated again unless the transistors 13 and 17 are in an OFF-state.Accordingly, before the circuit 10 at the kth stage operates, theelectric potentials of the terminal R and the electrode SR(k) should bereturned to the L level. This operation is referred to as ‘setoperation’ in this specification. The timing of performing the setoperation is arbitrary. The set operation of the kth stage may beperformed at a timing when the electric potential of the terminal P(k−1)at the (k−1)th stage rises. As a circuit configuration of this case, itis preferable that, as in FIGS. 1A and 1B, the terminal F and theelectrode SR(k) are connected using the transistor 16 of which gateelectrode is connected to the terminal P(k−1), one of the sourceelectrode and the drain electrode is connected to the terminal G, andthe other of the source electrode and the drain electrode is connectedto the terminal F.

In the case of using this configuration, since the electric potential ofterminal P(k−1) at the (k−1)th stage rises before a pulse is inputted tothe terminal IN at the kth stage, the transistor 16 at the (k−1)th stageis turned on at the timing. Thus, the electric potential of the terminalF becomes the L level. Therefore, the terminal R at the kth stage ischanged from the H level held to the L level, and thus, the transistors13 and 17 are turned OFF. After that, an output of the (k−1)th stage isinputted to the terminal IN at the kth stage; thus, the operation of thecircuit 10 at a kth stage starts.

Here, the gate electrode the transistor 16 at the (k−1)th stage may beconnected to the terminal OUT at the (k−1)th stage instead of beingconnected to the terminal F of the (k−1)th stage. In this case, setoperation of the kth stage is performed when the output of the (k−1)thstage is inputted to the terminal IN of the kth stage.

Further, set operation of the kth stage may be performed at a timingwhen the electric potentials of the terminal P(k−2) and the terminal OUTat the (k−2)th stage rise. Alternatively, the set operation may beperformed at a timing when the electric potentials of the terminalP(k−2) and the terminal OUT at a stage before the (k−2)th rise. With theconnection with a farther stage through the electrode SR, the length ofleading the electrode SR from the terminal R at the kth stage is madelonger than the pitch between the circuit 10 at the kth stage and thecircuit 10 at the (k+1)th stage; thereby, the value of parasiticcapacitance associated with the electrode SR can be made larger. It isthus advantageous that the electric potentials of the electrode SR andthe terminal R are ensured to be held.

A common timing pulse may be additionally inputted to all the stages toperform the set operation. Alternatively, the start pulse may be used asa common timing pulse. The electrode SR(1) at the first stage may beconnected to one of a source and a drain electrode of the transistor 18instead of being connected to the terminal F at the preceding stage.Thus, set operation of the first stage is performed when the start pulseis inputted.

Another circuit configuration of a shift register in this embodimentmode, in which the electric potential of the output terminal is fixedduring a non-selection period, and malfunctions due to clock signals andnoise are reduced, will be described below. An example of the shiftregister having a different circuit configuration according to thepresent invention is illustrated in FIGS. 2A to 2C. FIG. 2A illustratesa circuit configuration of the whole shift register of the presentinvention. FIG. 2B illustrates a configuration example of a circuit 20corresponding to a single stage circuit of the present invention. FIG.2C illustrates another circuit configuration of the whole shift registerusing the circuit 20 shown in FIG. 2B.

The circuit shown in FIG. 2A is provided with the start pulse terminalSP, the first clock signal line CLK1, the second clock signal line CLK2,the power supply line Vss, a transistor 28, and n pieces of the circuits10 (n is an integer greater than or equal to two), and an outputterminal L(k) (k is an integer from one to n inclusive) providedcorresponding to the circuit 20.

The circuit 20 shown in FIG. 2B is provided with terminals IN, OUT, G,R, F, B, C, and V, transistors 21, 22, 23, 25, 26, 27 a, 27 b, and 27 c,a capacitor element 24, and a terminal P. Here, the transistor 21 may bereplaced with another element having rectifying characteristics, whichis to be used as a rectifying element for input (a first rectifyingelement). Further, the transistor 25 may be another element havingrectifying characteristics, which is to be a rectifying element forreset(also referred to as second rectifying element). Further, thetransistor 22 is used as a transmission transistor (also referred to asa first transistor). The transistor 23 is used as an internal voltageclamp transistor (also referred to as a third transistor). Thetransistor 27 a is used as an output voltage clamp transistor (alsoreferred to as a second transistor). Still Further, the transistor 26 isused as a set transistor (also referred to as a fourth transistor):

Note that a terminal P of the circuit 20 at a kth stage is also referredto as a terminal P(k). Further, this embodiment mode specifies acapacitor element 24; however, functions of the capacitor element 24 canalso be realized by parasitic capacitance formed between a gateelectrode and a drain electrode (or a source electrode) of thetransistor 22. Therefore, the present invention includes not only thecase where the capacitor element 24 is formed as an electrical element,but also the case where the capacitor element 24 is a parasiticcapacitor element which is associated with the transistor 22. Thecircuit shown in FIG. 2C has a configuration in which a power supplyline Vdd is added to the circuit shown in FIG. 2A.

The gate electrode of transistor 21 of the circuit 20 shown in FIG. 2Bis connected to a terminal IN, one of a source electrode and a drainelectrode of the transistor 21 is connected to the terminal IN, and theother of the source electrode and the drain electrode of the transistor21 is connected to the terminal P. The gate electrode of the transistor22 is connected to the terminal P, one of the source electrode and thedrain electrode of the transistor 22 is connected to the terminal C, theother of the source electrode and the drain electrode of the transistor22 is connected to the terminal OUT.

Further, the gate electrode of the transistor 23 is connected to aterminal R, one of a source electrode and a drain electrode of thetransistor 23 is connected to a terminal G, and the other of the sourceelectrode and the drain electrode of the transistor 23 is connected tothe terminal P. Further, one of electrodes of the capacitor element 24is connected to the terminal P, the other of the electrodes of thecapacitor element 24 is connected to the terminal OUT.

The gate electrode of the transistor 25 is connected to a terminal OUT,one of a source electrode and a drain electrode of the transistor 25 isconnected to the terminal OUT, and the other of the source electrode andthe drain electrode of the transistor 25 is connected to a terminal B.Further, the gate electrode of the transistor 26 is connected to theterminal P, one of a source electrode and a drain electrode of thetransistor 26 is connected to a terminal G, and the other of the sourceelectrode and the drain electrode of the transistor 26 is connected to aterminal F.

Further, the gate electrode of the transistor 27 a is connected to theterminal Q, one of a source electrode and a drain electrode of thetransistor 27 a is connected to the terminal G, and the other of thesource electrode and the drain electrode of the transistor 27 a isconnected to the terminal OUT. The gate electrode of the transistor 27 bis connected to the terminal P, one of a source electrode and a drainelectrode of the transistor 27 b is connected to the terminal G, and theother of the source electrode and the drain electrode of the transistor27 b is connected to the terminal Q. The gate electrode of thetransistor 27 c is connected to the terminal V, one of a sourceelectrode and a drain electrode of the transistor 27 c is connected tothe terminal V, and the other of the source electrode and the drainelectrode of the transistor 27 c is connected to the terminal Q.

Next, the connection of the circuit 20 at the kth stage in the circuitshown in FIG. 2A will be described. The circuit shown in FIG. 2A has thesame configuration as the circuit shown in FIG. 1A except for theterminal V; thus, the same description will not be repeated. Theterminal V may be connected to a clock signal line which is differentfrom a clock signal line to which the terminal C is connected as shownin FIG. 2A. Although not shown, the terminal V may be connected to theclock signal line to which the terminal C is connected.

FIG. 2C shows a circuit in which a power supply line Vdd dedicated forconnecting the terminal V is added to the circuit shown in FIG. 2A. Asshown in FIG. 2C, the terminals V and the power supply lines Vdd of allthe stages may be connected. The potential applied to the power supplyline Vdd may be any electric potential as long as the electric potentialis higher than the L level by the sum of the threshold voltages of thetransistors 27 a and 27 c or more.

Next, input signals and output signals of the circuits shown in FIGS.2A, 2B, and 2C are the same as that of the FIG. 1C. A different point ofthe circuit shown in FIGS. 2A to 2C from the circuit shown in FIGS. 1Ato 1C is that the function of the transistor 17 in FIG. 1B for fixingthe electric potential of the terminal OUT to the L level is realized bythe transistors 27 a, 27 b, and 27 c. Specifically, the gate electrodeof the transmission transistor 22 and the gate electrode of the outputvoltage clamp transistor 27 a are connected to each other through acircuit for outputting an inverted signal.

In the circuit in FIG. 2B, when the circuit does not operate and theelectric potential of the terminal P is fixed at L level by thetransistor 23, the transistor 27 b is in an OFF-state. Here, since theelectric potential of the electrode Q is at H level, the transistor 27 ais in an ON-state. Specifically, when the terminal P is fixed at Llevel, the terminal OUT is also fixed at the L level, therebymalfunctions of the output terminal due to capacitive coupling with theclock signal line and the like will be reduced.

IN the case where the circuit 20 operates, since a pulse is inputted tothe terminal IN, and the electric potential of the point P rises, thetransistor 27 b is turned ON. Thus, the electric potential of theelectrode Q approximates the L level, thereby the transistor 27 a isturned OFF. Specifically, when the electric potential of the terminal Prises and the terminal OUT is conducted electricity to the terminal C,the transistor 27 a turned OFF. Thus, the circuit 20 can achieveoperation similar to the circuit 10 shown in FIGS. 1A to 1C.

Note that according to this embodiment mode, it is a merit of a shiftregister of the present invention, that the period during which theterminal OUT is fixed at the Low level is long. In other words, as theterminal OUT is fixed at the Low level for a longer time, themalfunctions of the terminal OUT due to operation of another signal lineor noise from the outside are reduced; thus, the stability in operationis high. Further, as to a shift register of the present invention,frequency of switching of the signals inputted to the transistorconnected to the terminal OUT is less; thus, the electric potential ofthe terminal OUT is hardly varied due to feed-through of signals, andhigh stability of operation can be achieved.

Embodiment Mode 2

In this embodiment mode, reset operation of the last stage and the resetoperation of all the stages of the shift register circuit of the presentinvention will be described.

In the circuit configuration described in Embodiment Mode 1, the resetoperation of the current stage is conducted at the timing of theoperation of the next stage. Here, since there is no stage after theshift register circuit at the last stage, no pulse defining the timingof the reset operation is inputted to the last stage. Therefore, theelectric potential of the electrode SR(n) will not be at H level byreset operation. Accordingly, clock signals are constantly outputted tothe terminal OUT of the last stage.

Considering the points, in Embodiment Mode 1, the electrode SR(n) isconnected to the electrode SR(n−1) as shown in FIG. 1A, FIG. 2A, andFIG. 2C. Thus, reset operation can be performed by making the electrodeSR(n) at H level with the output of the terminal OUT at the last stageitself. Accordingly, the electric potential of a clock signal line canbe prevented from being constantly outputted to the output terminal L(n)at the last stage can. In this case, the pulse width of the output ofthe last stage is smaller than the pulse width of the output of a clocksignal. Here, in the case of a circuit configuration in which clocksignals are constantly outputted to the last stage, and the output ofthe last stage is not used actively except for reset operation of thepreceding stage, excess power is consumed for charging or dischargingthe parasitic capacitance element connected to the output terminal ofthe last stage.

A configuration to be described in this embodiment mode is differentfrom the configuration shown in Embodiment Mode 1, in which the laststage can be operated as a shift register. FIGS. 3A, 3B, and 3C eachillustrate a configuration in which a transistor 29 which is used forreset operation of the last stage is added to each configuration shownin FIG. 1A, FIG. 2A, and FIG. 2C. The gate electrode of the transistor29 is connected to the start pulse terminal SP, one of a sourceelectrode and a drain electrode transistor 29 is connected to the startpulse terminal SP, the other of the source electrode and the drainelectrode of the transistor 29 is connected to the electrode SR(n).

Further, as shown in FIGS. 3A to 3C, in the case where the transistor 29is used for reset operation of the last stage, it is not necessary toperform reset operation of the last stage by the last stage itself, andreset operation can be performed at a timing when the start pulse isinputted; therefore, the electrode SR(n) and electrode SR(n−1) are notrequired to be connected.

FIG. 4 is a timing chart for explaining operation of the circuit shownin FIGS. 3A to 3C. A different point from FIG. 1C is that since resetoperation of the terminal P(n) of the last stage is performed at atiming when the start pulse is inputted (time T0), the output terminalL(n) of the last stage can also be operated as a shift register circuit.Here, in the timing chart in FIG. 4, when the period during which thestart pulse is inputted is T, the total number of pulses of the clocksignals, which are inputted during the period T is preferably greaterthan the number n of the stages in the shift register circuit. Thus,reset operation of the last stage can be securely operated during withinthe period T.

Next, referring to FIGS. 5A to 5C and FIG. 6, a shift register circuitof the present invention in which a signal line dedicated for resetoperation is added will be described.

FIGS. 5A, 5B, and 5C each illustrate a configuration in which a signalline RES dedicated for reset operation and a transistor RE(k) (k is aninteger from one to n inclusive) connected to the signal line RES areadded to the configuration each shown in FIG. 1A, FIG. 2A, and FIG. 2C.The gate electrode of the transistor RE(k) is connected to the signalline RES, one of a source electrode and a drain electrode of thetransistor RE(k) is connected to the signal line RES, the other of thesource electrode and the drain electrode of the transistor RE(k) isconnected to the electrode SR(k).

FIG. 5 and FIG. 6 illustrate shift register circuits, in which thetransistor RE(k) is additionally connected to each of the stages,thereby all the stages can be reset at any arbitrary timing, which canbe returned to an initial state before operating the last stage.However, the present invention is not limited to thereto, and the numberof the transistor REs(k) is arbitrary. For example, the transistor REmay be provided only on the last stage, the transistors RE may beprovided on only odd-numbered stages or only even-numbered stages, orthe transistor RE may be provided on the stages in only the first halfor only in the second half. There is an advantage in that the number ofthe transistors RE is reduced, the circuit scale becomes smalleraccordingly; thereby the percentage of the circuit taking up over thesubstrate is reduced. Further, when the number of the transistors RE isreduced, the load of driving the signal line RES is reduced and powerconsumption can be reduced, which is advantageous.

Here, referring to FIG. 6, an operation of a shift register circuit ofthe present invention in which a signal line dedicated for resetoperation is added will be described. FIG. 6 is a timing chart of changein the electric potentials of the input signal, the terminal P, and theoutput terminal L at time Tr when a pulse is inputted to a signal lineRES to reset all the stages. When a start pulse is inputted at the timeT0, the same operation as FIG. 1C is performed until a pulse is inputtedto the signal line RES. However, when a pulse is inputted to the signalline RES at the time Tr, electric potentials of the electrodes SR of allthe stages are at the stage H level; thus, the output terminal L and theterminal P are fixed at L level. Here, the transistor 16 or 26 forchanging the electric potential of the electrode SR into the L level isturned OFF because the electric potential of the terminal P becomes theL level. Accordingly, a path through which current flows from the signalline RES to the power supply line Vss when a pulse is inputted to thesignal line RES will not be formed.

Thus, as to the shift register circuits of the present invention inFIGS. 5A to 5C in each of which a signal line dedicated for resetoperation is added, all the stages can be reset at any arbitrary timing,which can be returned to an initial state before operating the laststage. In the case of using this shift register circuit as a drivercircuit of a display device, for example, only pixels arranged in a partof the display area are used, it is advantageous that pixels of an areanot to be used will not be used by stopping the operation of the shiftregister circuit, which results in a merit that power consumption can bereduced.

Further, when a pulse is inputted to the signal line RES, the floatedelectrode SR is charged, so that decrease in the electric potential ofthe electrode SR due to leakage current can be prevented. Specifically,there is an advantage that a transistor of which gate electrode isconnected to the electrode SR can easily be held at an ON-state.

Note that this embodiment mode can be freely combined with anotherembodiment mode.

Embodiment Mode 3

Voltage is applied between a gate electrode and a source electrode toturn a transistor ON. Here, if voltage is continuously applied to thegate electrode of the transistor, charges are trapped in energy levelsregions between the source electrode or the drain electrode and the gateelectrode due to an impurity or the like, and the trapped charges forman internal electric field; thus, change in characteristics over time iscaused. Especially, change of shifting of the threshold voltage(threshold shift) is caused. As to this change over time, not only thevoltage of the polarity for turning the transistor ON, but also thevoltage of the inverted polarity (also referred to as a reverse bias) isalso applied, thus, the trapped charges are discharged and the degree ofchange is known to decrease. The threshold shift is significantlyobserved in a thin film transistor using amorphous silicon in a channellayer, which has defect levels in a region between the source electrodeor the drain electrode and the gate electrode. Therefore, the shiftregister circuit of this embodiment mode is particularly advantageous ina thin film transistor using amorphous silicon in a channel layer.However, the present invention is not limited thereto.

In this embodiment mode, description will be given of operation ofapplying a reverse bias to a transistor forming a shift register circuitof the present invention.

First, FIGS. 7A to 7C illustrates shift register circuits in whichfunction of applying a reverse bias to reduce change in characteristicsover time is added to the circuits shown in FIGS. 1A to 1C. FIG. 7A isan overall view of a shift register circuit of the present invention,FIG. 7B illustrates one stage of a circuit 30 of the shift registercircuit of the present invention, and FIG. 7C is a timing chart of inputsignals and output signals of the shift register circuit of the presentinvention.

FIG. 7B shows a circuit in which transistors 39 a and 39 b, a terminalN, and an electrode S are added to a circuit shown in FIG. 1B. Further,transistors 31, 32, 35, 36, and 37 and a capacitor element 34 correspondto the transistors 11, 12, 15, 16, and 17 and the capacitor element 14in FIG. 1B respectively, the connection is the same as FIG. 1B Further,the gate electrode of the transistor 33 in FIG. 7B is connected to anelectrode S, one of a source electrode and a drain electrode of thetransistor 33 is connected to the terminal G, and the other of thesource electrode and the drain electrode of the transistor 33 isconnected to the terminal P.

Further, the gate electrode of the transistor 37 is connected to theelectrode S, one of a source electrode and a drain electrode of thetransistor 37 is connected to the terminal G, and the other of thesource electrode and the drain electrode of the transistor 37 isconnected to the terminal OUT. The gate electrode of the transistor 39 ais connected to the electrode S, one of a source electrode and a drainelectrode of the transistor 39 a is connected to the electrode S, andthe other of the source electrode and the drain electrode of thetransistor 39 a is connected to the terminal N. Further, the gateelectrode of the transistor 39 b is connected to the terminal N, one ofa source electrode and a drain electrode of the transistor 39 b isconnected to the electrode S, the other of the source electrode and thedrain electrode of the transistor 39 b is connected to the terminal R.

FIG. 7A illustrates a circuit in which a signal line RB connected to aterminal N of the circuit 30 in each stage is added to the circuit shownin FIG. 1A. Further, the transistor 38 corresponds to the transistor 18in FIG. 1A, and the connection is similar.

Here, operations of the circuits shown in FIGS. 7A and 7B with referenceto FIG. 7C. When a pulse is inputted to the start pulse terminal SP attime T0, the shift register circuit is operated, and output signals areoutputted sequentially from the output terminal L(1). Further, theperiod during which the output signals are outputted to an outputterminal L(n) is referred to as a normal operation period. During normaloperation period, the electric potential of the H level may be inputtedto the signal line RB. Here, the transistor 39 b is in an ON-state, andthe transistor 39 a is in an OFF-state. Specifically, the terminal R andthe electrode S are in conduction state, and the terminal N and theelectrode S are in non-conduction state; thus, the connection state inFIG. 7B is similar to that of FIG. 1B, thereby the shift registercircuits in FIGS. 7A to 7C operates in a like manner shown in FIGS. 1Ato 1C.

Next, as shown in FIG. 7C, after an output signal is outputted to theoutput terminal L(n) of the shift register circuit shown in FIG. 7A, theelectric potential of the signal line RB may be lowered between time T1and time 12. This period is referred to as a reverse bias applicationperiod. Thus, the transistor 39 b shown in FIG. 7B is turned OFF, andthe transistor 39 a is turned ON. That is, electrical continuity betweenthe terminal R and the electrode S is lost and electrical continuitybetween the terminal N and the electrode S is made; thus, the electricpotential of the electrode S is lowered. After that, when the electricpotential of the electrode S exceeds the electric potential of theelectrode N by the threshold voltage of the transistor 39 a, thetransistor 39 a is turned OFF, and lowering of the electric potential ofthe electrode S is stopped. Here, the electric potential of the signalline RB may be lower than the electric potential of the power supplyline Vss. When lower electric potential of the signal line RB is lowerthan the electric potential of the power supply line Vss, the electricpotential of the electrode S can be lowered further during the reversebias application period. Thus, the electric potential of the oppositepolarity to the case of an ON-state can be applied to the gateelectrodes of the transistors 33 and 37, thus, it is advantageous thatthe threshold shift of the transistor can be reduced.

Here, the transistor 39 b is a transistor having functions of providingelectrical continuity between the terminal R and the electrode S, duringthe normal operation period, and interrupting the electrical continuitybetween the terminal R and the electrode S during the reverse biasapplication period. In the case where the transistor 39 b is notprovided and electric continuity between the terminal R and theelectrode S is established continuously, the circuit scale is madesmaller, and since the value of parasitic capacitance connected to thesignal line RB is reduced, which results in reduction of the powerconsumption.

Further, when the transistor 39 b is disposed as shown in FIG. 7B, theelectric potential of the terminal N is lowered by the signal line RB,the electric potential of the terminal R can be prevented fromdecreasing at the same time as the electric potential of the electrode Sis lowered. Here, consider the case where the electrical continuity isestablished between the terminal R and the electrode S during thereverse bias application period, and the electric potential of theterminal R is also decreased with decrease of the electric potential ofthe electrode S. The terminal R is connected to the terminal F of thepreceding circuit 30 through the electrode SR; therefore, when theelectric potential of the terminal R is reduced to a potential lowerthan or equal to the electric potential of the power supply line Vssminus the threshold voltage of the transistor 36 in the preceding stage,the transistor 36 of the preceding stage is turned ON; thus, constantcurrent flows through the signal line RB and the power supply line Vss.Further, the terminal R is also connected to the circuit 30 at the nextstage through the electrode SR; therefore, when the electric potentialof the terminal R is reduced, the transistors 35 and 32 of the nextstage is turned ON; thus, constant current can be considered to flowthrough a clock signal line, the transistor 32, and the transistor 35 atthe next stage, and the transistor 39 a and the signal line RB at thecurrent stage. Accordingly, during the reverse bias application period,electrical continuity between the terminal R and the electrode S isinterrupted, thereby preventing the formation of a path of currentincluding the terminal R due to decrease in the electric potential ofthe terminal R. Thus, sufficient reverse bias can be applied to thetransistors 33 and 37 while reducing power consumption.

Note that in this embodiment mode, an example of applying a reverse biasto the gate electrodes of the transistors 33 and 37 during the reversebias application period is described; however, the present invention isnot limited thereto. A reverse bias may be applied to any of thetransistors. However, the transistors 33 and 37 are in an ON-stateduring most of the period during when the output terminal L should output the L level, and such transistors which are in an ON-state withlarge ratio of time will cause great degree of threshold shift.Accordingly, as shown in FIG. 7B, threshold shift should be reduced byconnecting the transistors 39 a and 39 b to the gate electrodes of thetransistors 33 and 37, and providing a reverse bias application period,which is effective and preferable.

First, FIGS. 8A to 8C illustrates circuits in which a function ofapplying a reverse bias to reduce change in characteristics over time isadded to the shift register circuit shown in FIGS. 2A to 2C. FIG. 8A isan overall view of a shift register circuit of the present invention,FIG. 8B illustrates one stage of a circuit 40 of the shift registercircuit of the present invention, and FIG. 8C is another overall viewthe shift register circuit of the present invention.

FIG. 8B shows a circuit in which transistors 49 a, 49 b, 49 c, and 49 d,a terminal N, an electrode S, and an electrode U are added to a circuitshown in FIG. 2B. Further, transistors 41, 42, 45, 46, 47 b, and 47 cand a capacitor element 44 correspond to the transistors 21, 22, 25, 26,27 b, and 27 c and the capacitor element 24 in FIG. 2B respectively, theconnection is the same as FIG. 2B. Further, the gate electrode of thetransistor 43 in FIG. 8B is connected to the electrode S, one of asource electrode and a drain electrode of the transistor 43 is connectedto the terminal and the other of the source electrode and the drainelectrode of the transistor 43 is connected to the terminal P.

Further, the gate electrode of the transistor 47 a is connected to theelectrode U, one of a source electrode and a drain electrode of thetransistor 47 a is connected to the terminal G, and the other of thesource electrode and the drain electrode of the transistor 47 a isconnected to the terminal OUT. The gate electrode of the transistor 49 ais connected to the electrode S, one of a source electrode and a drainelectrode of the transistor 49 a is connected to the electrode S, andthe other of the source electrode and the drain electrode of thetransistor 49 a is connected to the terminal N. Further, the gateelectrode of the transistor 49 b is connected to the terminal N, one ofa source electrode and a drain electrode of the transistor 49 b isconnected to the electrode R, and the other of the source electrode andthe drain electrode of the transistor 49 b is connected to the terminalS. The gate electrode of the transistor 49 c is connected to theterminal U, one of a source electrode and a drain electrode of thetransistor 49 c is connected to the electrode U, and the other of thesource electrode and the drain electrode of the transistor 49 c isconnected to the terminal N. Further, the gate electrode of thetransistor 49 d is connected to the terminal N, one of a sourceelectrode and a drain electrode of the transistor 49 d is connected tothe electrode Q, the other of the source electrode and the drainelectrode of the transistor 49 d is connected to the terminal U.

Here, FIG. 8A illustrates a circuit in which a signal line RB connectedto a terminal N of the circuit 40 in each stage is added to the circuitshown in FIG. 2A. Further, the transistor 48 corresponds to thetransistor 28 in FIG. 2A, and the connection is similar. Further, FIG.8C illustrates a circuit in which a power supply line Vdd is added tothe circuit shown in FIG. 8A, and the power supply line Vdd is connectedto the terminals V of the circuits 40 of all the stages.

Here, the circuits shown in FIGS. 8A, 8B, and 8C may be operated inaccordance with the timing chart shown in FIG. 7C. In the case ofoperating the circuits shown in FIGS. 8A, 8B, and 8C in accordance withthe timing chart shown in FIG. 7C, during normal operation period, theelectric potential of the H level may be inputted to the signal line RB.Here, the transistors 49 b and 49 d are in an ON-state, and thetransistors 49 a and 49 c are in an OFF-state. Specifically, theterminal R and the electrode S, and the terminal Q and the electrode Uare in a conduction state, and the terminal N and the electrode S, andthe electrode N and the electrode U are in a non-conduction state; thus,the connection state in FIG. 8B is similar to that of FIG. 2B, therebythe shift register circuits in FIGS. 8A to 8C operates in a like mannershown in FIGS. 2A to 2C.

Next, during the reverse bias application period, the transistors 49 band 49 d shown in FIG. 8B are turned OFF, and the transistors 49 a and49 c are turned ON. That is, the terminal R and the electrode S, and theterminal Q and the electrode U are in the non-conduction state, and theterminal N and the electrode S, and the electrode N and the electrode Uare in the conduction state; thus, the electric potentials of theelectrode S and the electrode U drop. After that, when the electricpotentials of the electrode S and the electrode U exceed the electricpotential of the electrode N by the threshold voltage of the transistors49 a and 49 c are turned OFF, and lowering of the electric potential ofthe electrodes S and U is stopped. Here, the electric potential of thesignal line RB may be lower than the electric potential of the powersupply line Vss. When lower electric potential of the signal line RB islower than the electric potential of the power supply line Vss, theelectric potentials of the electrode S and the electrode U can belowered further during the reverse bias application period. Thus, theelectric potential of the opposite polarity to the case of an ON-statecan be applied to the gate electrodes of the transistors 43 and 47 a,thus, it is advantageous that the threshold shift of the transistor canbe reduced.

Here, the transistors 49 b and 49 d are transistors having functions ofproviding conduction state of the terminal R and the electrode S, andthe electrode Q and the electrode U during the normal operation period,and non-conduction state of the terminal R and the electrode S, and theelectrode Q and the electrode U during the reverse bias applicationperiod. In the case where the transistors 49 b and 49 d are not providedand the terminal R and the electrode S, and the electrode Q and theelectrode U are in the conduction state continuously, the circuit scaleis made smaller, and since the value of parasitic capacitance connectedto the signal line RB is reduced, which results in reduction of thepower consumption.

Further, when the transistors 49 b and 49 d are disposed as shown inFIG. 8B, the electric potential of the terminal N is lowered by thesignal line RB, the electric potentials of the terminal R and theelectrode O can be prevented from decreasing at the same time as theelectric potentials of the electrode S and the electrode U are lowered.

Here, consider the case where the terminal R and the electrode S are inthe conduction state during the reverse bias application period, and theelectric potential of the terminal R is also decreased with decrease ofthe electric potential of the electrode S. The terminal R is connectedto the terminal F of the preceding circuit 40 through the electrode SR;therefore, when the electric potential of the terminal R is reduced to apotential lower than or equal to the electric potential of the powersupply line Vss minus the threshold voltage of the transistor 46 in thepreceding stage, the transistor 46 of the preceding stage is turned ON;thus, constant current flows through the signal line RB and the powersupply line Vss. Further, the terminal R is also connected to atransistor 45 of the circuit 40 at the next stage through the electrodeSR; therefore, when the electric potential of the terminal R is reduced,the transistors 45 and 42 of the next stage is turned ON; thus, constantcurrent can be considered to flow through a clock signal line, thetransistor 42, and the transistor 45 at the next stage, and thetransistor 49 a and the signal line RB at the current stage.

Further, consider the case where the terminal Q and the electrode U arein the conduction state during the reverse bias application period, andthe electric potential of the terminal Q is also decreased with decreaseof the electric potential of the electrode U. Since the electrode Q isconnected to a source electrode or a drain electrode of the transistors47 b and 47 c, when the electric potential of the electrode Q isreduced, the transistors 47 b and 47 c are in an ON-state, so thatconstant current flows from the terminal G and the terminal V throughthe electrode Q, the transistor 49 d, the electrode U, the transistor 49c, and the terminal N.

Accordingly, during the reverse bias application period, the terminal Rand the electrode S, and the electrode Q and the electrode U are in thenon-conduction state with the transistors 49 b and 49 d, therebypreventing the formation of a path of current including the terminal Rand the electrode Q due to decrease in the electric potentials of theterminal R and the electrode Q. Thus, sufficient reverse bias can beapplied to the transistors 43 and 47 a while reducing power consumption.Note that both the transistors 49 b and 49 d may be provided, only oneof them may be provided, or neither of them may be provided.

Note that in this embodiment mode, an example of applying a reverse biasto the gate electrodes of the transistors 43 and 47 a during the reversebias application period is described; however, the present invention isnot limited thereto. A reverse bias may be applied to any of thetransistors. However, the transistors 43 and 47 a are in an ON-stateduring most of the period during when the output terminal L should output the L level, and such transistors which are in an ON-state withlarge ratio of time will cause great degree of threshold shift.Accordingly, as shown in FIG. 8B, threshold shift should be reduced byconnecting the transistors 49 a, 49 b, 49 c, and 49 d to the gateelectrodes of the transistors 43 and 47 a, and providing a reverse biasapplication period, which is effective and preferable.

As described above, in this embodiment mode, threshold shift of thetransistors 33, 37, and 43, 43 a can be reduced by connecting thetransistors 39 a, 39 b, 49 a, 49 b, 49 c, and 49 d for applying reversebias to the gate electrodes of the transistors 33, 37, 43, and 47 a.Further, a gate electrode of an arbitrary transistor of an arbitrarycircuit in addition to the circuit shown in this embodiment mode may beconnected to a circuit shown in FIGS. 9A to 9D, thereby applying areverse bias to the transistor. Due to the circuits shown in FIGS. 9A to9D, the electric potential of any electrode in the circuit other thanthe gate electrode of the transistor is not changed; thus, thresholdshift of the transistor can be reduced without constant current flow ormalfunctions.

The circuits shown in FIGS. 9A to 9D are each provided with a signalterminal SIG, a bias terminal BIAS, an object terminal GATE, a cut-offtransistor SIG-Tr, and a bias transistor BIAS-Tr. Here, the biastransistor BIAS-Tr in each of the circuits shown in FIGS. 9A to 9D andFIGS. 10A to 10H are used as a rectifying element.

In the circuits shown in FIGS. 9A, 9B, 9C, and 9D, the gate electrode ofthe cut-off transistor SIG-Tr is connected to the bias terminal BIAS,one of a source electrode and a drain electrode of the cut-offtransistor SIG-Tr is connected to the signal terminal SIG and the otherof the source electrode and the drain electrode of the cut-offtransistor SIG-Tr is connected to the object terminal GATE.

In the circuits shown in FIGS. 9A and 9D, the gate electrode of the biastransistor BIAS-Transistor is connected to the object terminal GATE, oneof a source electrode and a drain electrode of the bias transistorBIAS-Tr is connected to the object terminal GATE, the other of thesource electrode and the drain electrode of the bias transistor BIAS-Tris connected to the bias terminal BIAS.

In the circuits shown in FIGS. 9B and 9C, the gate electrode of the biastransistor BIAS-Tr is connected to the bias terminal BIAS, one of asource electrode and a drain electrode of the bias transistor BIAS-Tr isconnected to the object terminal GATE, and the other of the sourceelectrode and the drain electrode of the bias transistor BIAS-Tr isconnected to the bias terminal BIAS.

The object terminal GATE is connected to a transistor which applies areverse bias. It is appropriate to apply a reverse bias to both betweenthe gate electrode and a source electrode of the transistor, and betweenthe gate electrode and a drain electrode of the transistor. Therefore,it is preferable to connect the object terminal GATE to the gateelectrode of the transistor which applies a reverse bias. However, thepresent invention is not limited thereto, and the object terminal GATEmay be connected to the source electrode or the drain electrode of thetransistor which applies a reverse bias. At that time, the polarity ofthe bias to be applied as a reverse bias may be opposite to the casewhere the object terminal GATE is connected to the gate electrode. Notethat the number of transistors connected to the object terminal GATE isarbitrary.

The signal terminal SIG is connected to a signal line or a power supplyline inputted to the transistor when the transistor is normallyoperated. The bias terminal BIAS is a signal line for selecting whetherto apply a reverse bias to the transistor, or to transmit the electricpotential of an electrode connected to the signal terminal SIG to theobject terminal GATE.

Here, the circuits shown in FIGS. 9A, 9B, 9C, and 9D are classified withrespect to the polarity of the cut-off transistor SIG-Transistor and thepolarity of the bias transistor BIAS-Tr.

FIGS. 9A and 9B illustrate circuits in which the electric potential ofan H level is applied to the bias terminal BIAS at a time of the normaloperation, and the electric potential of L level is applied to the biasterminal BIAS at a time of applying a reverse bias. For example, thecircuits can be used when the electrode to which a reverse bias isapplied is the gate electrode of an n-channel transistor.

FIGS. 9C and 9D are circuits in which the electric potential of an Llevel is applied to the bias terminal BIAS at a time of the normaloperation, and the electric potential of H level is applied to the biasterminal BIAS at a time of applying a reverse bias. For example, thecircuits can be used when the electrode to which a reverse bias isapplied is the gate electrode of a p-channel transistor. Thus, using acircuit shown in FIGS. 9A to 9D in this embodiment mode, a reverse biascan be applied to the gate electrode of any transistor in any circuitwithout changing the electric potentials of other electrodes in thecircuit.

Next, the case where a transistor to which a reverse bias is applied isincluded in the circuits shown in FIGS. 9A to 9D will be described withreference to FIGS. 10A to 10H.

FIG. 10A illustrates a circuit including a transistor AC-Tr to which areverse bias is applied is added to the circuit shown in FIG. 9A. Asshown in FIG. 10A, the gate electrode of the transistor AC-Tr may beconnected to the object terminal GATE of the circuit shown in FIG. 9A.FIG. 10B illustrates a circuit in which transistors AC-Tr1 and AC-Tr2 towhich a reverse bias is applied are included in the circuit shown inFIG. 9A. As shown in FIG. 10B, the gate electrodes of the transistorsAC-Tr1 and AC-Tr2 may be connected to the object terminal GATE in thecircuit shown in FIG. 9A.

Here, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may constitute a part ofa circuit having a certain function as the whole as with the transistors33 and 37 in FIGS. 7A to 7C or the transistors 43 and 47 a in FIG. 8A to8C, the circuit of the present invention in which a reverse bias isapplied is not dependent on where one of each source electrode and eachdrain electrode of the transistors AC-Tr, AC-Tr1, and AC-Tr2. Further,the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be N-channel transistors.Thus, in a period during which an H level is inputted to the biasterminal BIAS, a signal inputted to a signal terminal SIG is inputted tothe transistor AC-Tr, AC-Tr1, and AC-Tr2, and in a period during whichthe L level is inputted to the bias terminal BIAS, the electricpotential dependent on the electric potential of the L level is appliedto the gate electrodes of the transistor AC-Tr, AC-Tr1, and AC-Tr2;thus, a reverse bias can be applied.

Further, FIG. 10C illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied in addition to the circuit shown in FIG.9B. As shown in FIG. 10C, the gate electrode of the transistor AC-Tr maybe connected to the object terminal GATE of the circuit shown in FIG.9B. Further, FIG. 10D illustrates a circuit in which transistors AC-Tr1and AC-Tr2 to which a reverse bias is applied are included in thecircuit shown in FIG. 9B. As shown in FIG. 10D, the gate electrodes ofthe transistors AC-Tr1 and AC-Tr2 may be connected to the objectterminal GATE in the circuit shown in FIG. 9B. Here, the transistorsAC-Tr, AC-Tr1, and AC-Tr2 may constitute a part of a circuit having acertain function as the whole as with the transistors 33 and 37 in FIGS.7A to 7C or the transistors 43 and 47 a in FIG. 8A to 8C, the circuit ofthe present invention in which a reverse bias is applied is notdependent on where one of each source electrode and each drain electrodeof the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be N-channeltransistors. Thus, in a period during which an H level is inputted tothe bias terminal BIAS the period, a signal inputted to a signalterminal SIG is inputted to the transistor AC-Tr, AC-Tr1, and AC-Tr2,and in a period during which the L level is inputted to the biasterminal BIAS, the electric potential dependent on the L level isapplied to the gate electrodes of the transistors AC-Tr, AC-Tr1, andAC-Tr2; thus, a reverse bias can be applied.

Further, FIG. 10E illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied in addition to the circuit shown in FIG.9C. As shown in FIG. 10E, the gate electrode of the transistor AC-Tr maybe connected to the object terminal GATE of the circuit shown in FIG.9C. Further, FIG. 10F illustrates a circuit in which transistors AC-Tr1and AC-Tr2 to which a reverse bias is applied are included in thecircuit shown in FIG. 9C. As shown in FIG. 10F, the gate electrodes ofthe transistors AC-Tr1 and AC-Tr2 may be connected to the objectterminal GATE in the circuit shown in FIG. 9C.

Here, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may constitute a part ofa circuit having a certain function as the whole as with the transistors33 and 37 in FIGS. 7A to 7C or the transistors 43 and 47 a in FIG. 8A to8C, the circuit of the present invention in which a reverse bias isapplied is not dependent on where one of each source electrode and eachdrain electrode of the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be P-channeltransistors. Thus, in a period during which an L level is inputted tothe bias terminal BIAS, a signal inputted to a signal terminal SIG isinputted to the transistor AC-Tr, AC-Tr1, and AC-Tr2, and in the periodduring which the H level is inputted to the bias terminal BIAS, theelectric potential dependent on the H level is applied to the gateelectrodes of the transistor AC-Tr, AC-Tr1, and AC-Tr2; thus, a reversebias can be applied.

Further, FIG. 10G illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied in addition to the circuit shown in FIG.9D. As shown in FIG. 10G, the gate electrode of the transistor AC-Tr maybe connected to the object terminal GATE of the circuit shown in FIG.9D.

Further, FIG. 10H illustrates a circuit in which transistors AC-Tr1 andAC-Tr2 to which a reverse bias is applied are included in the circuitshown in FIG. 9D. As shown in FIG. 10H, the gate electrodes of thetransistors AC-Tr1 and AC-Tr2 may be connected to the object terminalGATE in the circuit shown in FIG. 9D. Here, the transistors AC-Tr,AC-Tr1, and AC-Tr2 may constitute a part of a circuit having a certainfunction as the whole as with the transistors 33 and 37 in FIGS. 7A to7C or the transistors 43 and 47 a in FIG. 8A to 8C, the circuit of thepresent invention in which a reverse bias is applied is not dependent onwhere one of each source electrode and each drain electrode of thetransistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be P-channeltransistors. Thus, in a period during which an L level is inputted tothe bias terminal BIAS, a signal inputted to a signal terminal SIG isinputted to the transistor AC-Tr, AC-Tr1, and AC-Tr2, and in the periodduring which the H level is inputted to the bias terminal BIAS, theelectric potential dependent on the H level is applied to the gateelectrodes of the transistor AC-Tr, AC-Tr1, and AC-Tr2; thus, a reversebias can be applied.

Next, referring to FIGS. 11A to 11C and FIG. 12, a shift registercircuit of the present invention in which a signal line dedicated forreset operation is added to the circuits illustrated in FIG A, FIG. 8A,and FIG. 8C in which a reverse bias can be applied will be described.

FIGS. 11A, 11B, and 11C each illustrate a configuration in which asignal line RES dedicated for reset operation and a transistor RE(k) (kis an integer from one to n inclusive) connected to the signal line RESare added to the configuration each shown in FIG. 7A, FIG. 8A, and FIG.8C. The gate electrode of the transistor RE(k) is connected to thesignal line RES, one of a source electrode and a drain electrode of thetransistor RE(k) is connected to the signal line RES, and the other ofthe source electrode and the drain electrode of the transistor RE(k) isconnected to the electrode SR(k).

FIGS. 11A to 11C illustrate shift register circuits, in which thetransistor REk) is additionally connected to each of the stages, therebyall the stages can be reset at any arbitrary timing, which can bereturned to an initial state before operating the last stage. However,the present invention is not limited to thereto, and the number of thetransistor REs(k) is arbitrary. For example, the transistor RE may beprovided only on the last stage, the transistors RE may be provided ononly odd-numbered stages or only even-numbered stages, or the transistorRE may be provided on the stages in only the first half or only in thesecond half. There is an advantage in that the number of the transistorsRE is reduced, the circuit scale becomes smaller accordingly; therebythe percentage of the circuit taking up over the substrate is reduced.Further, when the number of the transistors RE is reduced, the load ofdriving the signal line RES is reduced and power consumption can bereduced, which is advantageous.

Here, referring to FIG. 12, an operation of a shift register circuit ofthe present invention in which a signal line dedicated for resetoperation is added will be described. FIG. 12 is a timing chart ofchange in the electric potentials of the input signal SP, the terminal P(not shown in the timing chart), and the output terminal L at time T1when a pulse is inputted to a signal line RES to reset all the stagesand at time T2 when the electric potential of the signal line RB isreduced to conduct a reverse bias application operation. When a startpulse is inputted at the time T0, the same operation as FIG. 1C isperformed until a pulse is inputted to the signal line RES. However,when a pulse is inputted to the signal line RES at the time T1, electricpotentials of the electrodes SR of all the stages are at the stage Hlevel; thus, the output terminal L and the terminal P are fixed at Llevel. Here, the transistor 36 or 46 for changing the electric potentialof the electrode SR into the L level is turned OFF because the electricpotential of the terminal P becomes the L level. Accordingly, a paththrough which current flows from the signal line RES to the power supplyline Vss when a pulse is inputted to the signal line RES will not beformed.

After that, during a period between time T2 and time T3, a reverse biascan be applied by reducing the electric potential of the signal line RB.Here, the electric potential of the signal line RB is preferably lowerthan the electric potential of the power supply line Vss. Further, theelectric potentials of the signal line RB and the signal line RES may beset at H level in order to later operate reset operation again during aperiod between time T3 and time T4. When thus another reset operation isperformed after applying a reverse bias, the electric potentials of theelectrode S, the terminal R, the electrode SR are set at H level;accordingly, the electric potential of the output terminal L is fixed atL level, thereby the period during which change in the electricpotential of output is suppressed can be extended.

Thus, as to the shift register circuits of the present invention inFIGS. 11A to 11C in each of which a signal line dedicated for resetoperation is added, all the stages can be reset at any arbitrary timing,which can be returned to an initial state before operating the laststage and a reverse bias can be applied at any arbitrary timing. In thecase of using this shift register circuit as a driver circuit of adisplay device, for example, only pixels arranged in a part of thedisplay area are used, it is advantages that pixels of an area not to beused will not be used by stopping the operation of the shift registercircuit, which results in a merit that power consumption can be reducedand the threshold shift of the transistor can be reduced. Further, whena pulse is inputted to the signal line RES, the floated electrode SR ischarged, so that decrease in the electric potential of the electrode SRdue to leakage current can be prevented. Specifically, there is anadvantage that a transistor of which gate electrode is connected to theelectrode SR can easily be held at an ON-state.

Next, referring to FIGS. 13A to 13C, description is given of a circuitwhich can conduct reset operation in addition to reverse bias operationby adding only one signal line to the shift register circuit shown inFIGS. 7A to 7C in which a revere bias can be applied.

FIG. 13A is an overall view of a shift register circuit of the presentinvention, FIG. 13B illustrates one stage of a circuit 50 of the shiftregister circuit of the present invention, and FIG. 13C is a timingchart of input signals and output signals of the shift register circuitof the present invention.

FIG. 13B illustrates a circuit in which the connection of the transistor39 a (corresponding to a transistor 59 a) is modified from and aterminal M is added to the circuit shown in FIG. 7B. Here, transistors51, 52, 53, 55, 56, 57, and 59 b and a capacitor element 54 correspondto the transistors 31, 32, 33, 35, 36, 37, and 39 b and the capacitorelement 34 in FIG. 7B respectively, and the connections are the same asthat shown in FIG. 7B. Further, the gate electrode of the transistor 59a in FIG. 13B of which connection has been modified is connected to theterminal M, one of a source electrode and a drain electrode of thetransistor 59 a is connected to the electrode S, and the other of thesource electrode and the drain electrode of the transistor 59 a isconnected to the terminal N.

FIG. 13A illustrates a circuit in which the signal line RB of thecircuit shown in FIG. 7A is replaced with a signal line BL and a signalline BE connected to a terminal M of the circuit 50 in each stage isadded to the circuit shown in FIG. 7A. Further, the transistor 58corresponds to the transistor 38 in FIG. 7A, and the connection issimilar.

Here, operations of the circuits shown in FIGS. 13A and 13B will beexplained with reference to FIG. 13C. During normal operation period,the electric potential of the H level may be inputted to the signal lineBL and the electric potential of the L level may be inputted to thesignal line BE. Here, the transistor 59 b is in an ON-state, and thetransistor 59 a is in an OFF-state. Specifically, the terminal R and theelectrode S are in the conduction state, and the terminal N and theelectrode S are in the non-conduction state; thus, the connection statein FIG. 13B is similar to that of FIG. 1B, thereby the shift registercircuits in FIGS. 13A to 13C operates in a like manner shown in FIGS. 1Ato 1C.

Next, as shown in FIG. 13C, after the normal operation period of theshift register circuit shown in FIG. 13A is finished, the electricpotential of the signal line BE may be increased between time T1 andtime T4. This period is referred to as a bias enable period. In the biasenable period, the transistor 59 a is in an ON-state. Periods in thebias enable period, in which the electric potential of the signal lineBL is at H level (between time T1 and time T2, and between time T3 andT4) are referred to as reset periods. In the reset periods, thetransistors 59 a and 59 b are in an ON-state, and the electric potentialof the terminal N is at H level; therefore, the electric potentials ofthe electrode S, the terminal R, and the electrode SR to which theterminal R is connected become H level. That is, reset operation can beperformed. Further, in the bias enable period, the period during whichthe electric potential of the signal line BL is at L level (between timeT2 and time T3) is a reverse bias application period. In the reversebias application period, the transistor 59 b in FIG. 13B is turned OFF,and the transistor 59 a is turned ON. Specifically, the terminal R andthe electrode S are in the non-conduction state, and the terminal N andthe electrode S are in the conduction state, thereby the electricpotential of the electrode S becomes L level in accordance with theelectric potential of the electrode N. Thereupon, since the transistor59 b is in the non-conduction state, the electric potential of theterminal N does not transmitted to the terminal R. Here, the electricpotential of the signal line BL may be lower than the electric potentialof the power supply line Vss. If the lower electric potential of thesignal line BL is lower than the electric potential of the power supplyline Vss, the electric potential of the electrode S can be made furtherlower in the reverse bias application period. Thus, the electricpotential which is has the opposite polarity to the case of ON-state canbe applied to the gate electrodes of the transistors 53 and 57, therebythe threshold shift of the transistors can be reduced.

As described above, as to the shift register circuit of the presentinvention shown in FIGS. 13A to 13C, normal operation periods and biasenable periods can be arbitrarily provided by the signal line BE.Further, in the bias enable period, if the electric potential of thesignal line BL is at H level, the circuit 50 can be subjected to resetoperation; meanwhile, the electric potential of the signal line BL is atL level, a reverse bias can be applied to the transistors 53 and 57.Moreover, lowering of the electric potential of the signal line BL doesnot change the potentials of other electrodes than the electrode S;thus, troubles such as flowing of constant current and malfunctions canbe reduced. Note that in the bias enable period, the electric potentialof the electrode S can be set freely.

Next, referring to FIGS. 14A to 14C, description is given of a circuitwhich can conduct reset operation in addition to reverse bias operationby adding only one signal line to the shift register circuit shown inFIGS. 8A to 8C in which a revere bias can be applied.

FIG. 14A is an overall view of a shift register circuit of the presentinvention, FIG. 14B illustrates one stage of a circuit 60 of the shiftregister circuit of the present invention, and FIG. 14C is anotheroverall view of the shift register circuit of the present invention.FIG. 14B illustrates a circuit in which the connection of the transistor39 a (corresponding to a transistor 59 a) is modified from and aterminal M is added to the circuit shown in FIG. 7B. Further,transistors 61, 62, 63, 65, 66, 67 a, 67 b, 67 c, 69 b, and 69 d and acapacitor element 64 correspond to the transistors 41, 42, 43, 45, 46,47 a, 47 b, 47 c, 49 b, and 49 d, and the capacitor element 44 in FIG.8B respectively, and the connections are the same as that shown in FIG.8B.

Further, the gate electrode of the transistor 69 a in FIG. 14B isconnected to the terminal M, one of a source electrode and a drainelectrode of the transistor 69 a is connected to the electrode S, andthe other of the source electrode and the drain electrode of thetransistor 69 a is connected to the terminal N. The gate electrode ofthe transistor 69 c is connected to the terminal M, one of a sourceelectrode and a drain electrode of the transistor 69 a is connected tothe electrode U, and the other of the source electrode and the drainelectrode of the transistor 69 a is connected to the terminal N.

Here, FIG. 14A illustrates a circuit in which a signal line RB connectedto a terminal N of the circuit 40 in each stage is added to the circuitshown in FIG. 8A. Further, the transistor 68 corresponds to thetransistor 48 in FIG. 8A, and the connection is similar. Further, FIG.14C illustrates a circuit in which a power supply line Vdd is added tothe circuit shown in FIG. 14A, and the power supply line Vdd isconnected to the terminal V of the circuits 60 of all the stages.

Here, the circuits shown in FIGS. 14A, 14B, and 14C may be operated inaccordance with the timing chart shown in FIG. 13C. In the case ofoperating the circuits shown in FIGS. 14A, 14B, and 14C in accordancewith the timing chart shown in FIG. 13C, during normal operation period,the electric potential of the H level may be inputted to the signal lineBL and the electric potential of the L level may be inputted to thesignal line BE. Here, the transistors 69 b and 69 d are in an ON-state,and the transistors 69 a and 69 c are in an OFF-state. Specifically, theterminal R and the electrode S, and the terminal Q and the electrode Uare in the conduction state, and the terminal N and the electrode S, andthe electrode N and the electrode U are in the non-conduction state;thus, the connection state in FIG. 14B is similar to that of FIG. 2B,thereby the shift register circuits in FIGS. 14A to 14C operates in alike manner shown in FIGS. 2A to 2C.

Next, during the bias enable period, a reset period can be provided byincreasing the electric potential of the signal line BL to the H level,and a reverse bias application period can be provided by reducing theelectric potential of the signal line BL to the L level. In the resetperiod, the transistors 69 a, 69 b, 69 c, and 69 d are all turned ON,and the terminal N at H level; thus, the circuit 60 is reset. On theother hand, in FIG. 14B, in the reverse bias application period, thetransistors 69 b and 69 d are turned OFF, and the transistors 69 a and69 c are turned ON. That is, the terminal R and the electrode S, and theterminal Q and the electrode U are in the non-conduction state, and theterminal N and the electrode S, and the electrode N and the electrode Uare in the conduction state; thus, since the electric potential of theterminal N is low, the electric potentials of the electrode S and theelectrode U become low. Here, the electric potential of the signal lineBL may be lower than the electric potential of the power supply lineVss. When lower electric potential of the signal line BL is lower thanthe electric potential of the power supply line Vss, the electricpotential of the electrode S can be lowered further during the reversebias application period. Thus, the electric potential of the oppositepolarity to the case of an ON-state can be applied to the gateelectrodes of the transistors 63 and 67 a, thus, the threshold shift ofthe transistor can be reduced.

As described above, as to the shift register circuit of the presentinvention shown in FIGS. 14A to 14C, normal operation periods and biasenable periods can be arbitrarily provided by the signal line BE.Further, in the bias enable period, if the electric potential of thesignal line BL is at H level, the circuit 60 can be subjected to resetoperation; meanwhile, the electric potential of the signal line BL is atL level, a reverse bias can be applied to the transistors 63 and 67 a.Moreover, lowering of the electric potential of the signal line BL doesnot change the potentials of other electrodes than the electrode S andthe electrode U; thus, troubles such as flowing of constant current andmalfunctions can be reduced. Note that in the bias enable period, theelectric potentials of the electrode S and the electrode U can be setfreely.

Here, the gate electrode of an arbitrary transistor of an arbitrarycircuit in addition to the circuit shown in FIGS. 13A to 13C and 14A to14C may be connected to a circuit shown in FIGS. 15A to 15D, therebyapplying a forward bias in addition to a reverse bias to the transistor.Due to the circuits shown in FIG. 15A to 15D, the electric 20 potentialof any electrode in the circuit other than the gate electrode of thetransistor is not changed when a reverse bias is applied; thus,threshold shift of the transistor can be reduced without constantcurrent flow or malfunctions. When a forward bias is applied, thecut-off transistor SIG-Tr turns ON; thus, the electric potential of anelectrode connected to the signal terminal SIG and the signal terminalSIG can be initialized or reset.

The circuits shown in FIGS. 15A to 15D are each provided with a signalterminal SIG, a bias terminal BIAS, an object terminal GATE, a cut-offtransistor SIG-Tr, and a bias transistor BIAS-Tr. In the circuits shownin FIGS. 15A, 15B, 15C, and 15D, the gate electrode of the cut-offtransistor SIG-Tr is connected to the bias terminal BIAS, one of asource electrode and a drain electrode of the cut-off transistor SIG-Tris connected to the signal terminal SIG, and the other of the sourceelectrode and the drain electrode of the cut-off transistor SIG-Tr isconnected to the object terminal GATE.

In the circuits shown in FIGS. 15A, 15B, 15C, and 15D, the gateelectrode of the bias transistor BIAS-Tr is connected to the selectionterminal BE-SW, one of a source electrode and a drain electrode of thebias transistor BIAS-Tr is connected to the object terminal GATE, andthe other of the source electrode and the drain electrode of the biastransistor BIAS-Tr is connected to the bias terminal BIAS.

The object terminal GATE is connected to a transistor which applies areverse bias. It is appropriate to apply a reverse bias to both betweenthe gate electrode and a source electrode of the transistor, and betweenthe gate electrode and a drain electrode of the transistor. Therefore,it is preferable to connect the object terminal GATE to the gateelectrode of the transistor which applies a reverse bias. However, thepresent invention is not limited thereto, and the object terminal GATEmay be connected to the source electrode or the drain electrode of thetransistor which applies a reverse bias. At that time, the polarity ofthe bias to be applied as a reverse bias may be opposite to the casewhere the object terminal GATE is connected to the gate electrode. Notethat the number of transistors connected to the object terminal GATE isarbitrary.

The signal terminal SIG is connected to a signal line or a power supplyline inputted to the transistor when the transistor is normallyoperated. The selection terminal BE-SW is a signal line for selectingwhether or not transmitting the electric potential of the bias terminalBIAS to the object terminal GATE. The bias terminal BIAS is a signalline for controlling an electric potential applied to the objectterminal GATE when the bias transistor BIAS-Tr is in an ON-state. Whenthe bias transistor BIAS-Tr is in an OFF-state, the bias terminal BIASis used for controlling whether to make or break electrical continuitybetween the signal terminal SIG and the object terminal GATE.

Here, the circuits shown in FIGS. 15A, 15B, 15C, and 15D are classifiedwith respect to the polarity of the cut-off transistor SIG-Tr and thepolarity of the bias transistor BIAS-Tr.

FIG. 15A illustrates a circuit in which the electric potential of the Hlevel is applied to the bias terminal BIAS and the electric potential ofthe L level is applied to the selection terminal BE-SW at a time of thenormal operation, the electric potential of the H level is applied tothe bias terminal BIAS and the electric potential of the H level isapplied to the selection terminal BE-SW at a time of reset operation,and the electric potential of L level is applied to the bias terminalBIAS and the electric potential of the H level is applied to theselection terminal BE-SW at a time of applying a reverse bias. Forexample, the circuit can be used when the electrode to which a reversebias is applied is the gate electrode of an n-channel transistor.

FIG. 15B illustrates a circuit in which the electric potential of the Hlevel is applied to the bias terminal BIAS and the electric potential ofthe H level is applied to the selection terminal BE-SW at a time of thenormal operation, the electric potential of the H level is applied tothe bias terminal BIAS and the electric potential of the L level isapplied to the selection terminal BE-SW at a time of reset operation,and the electric potential of L level is applied to the bias terminalBIAS and the electric potential of the L level is applied to theselection terminal BE-SW at a time of applying a reverse bias. Forexample, the circuit can be used when the electrode to which a reversebias is applied is the gate electrode of an n-channel transistor.

FIG. 15C illustrates a circuit in which the electric potential of the Llevel is applied to the bias terminal BIAS and the electric potential ofthe L level is applied to the selection terminal BE-SW at a time of thenormal operation, the electric potential of the L level is applied tothe bias terminal BIAS and the electric potential of the H level isapplied to the selection terminal BE-SW at a time of reset operation,and the electric potential of H level is applied to the bias terminalBIAS and the electric potential of the H level is applied to theselection terminal BE-SW at a time of applying a reverse bias. Forexample, the circuit can be used when the electrode to which a reversebias is applied is the gate electrode of a P-channel transistor.

FIG. 15D illustrates a circuit in which the electric potential of the Llevel is applied to the bias terminal BIAS and the electric potential ofthe H level is applied to the selection terminal BE-SW at a time of thenormal operation, the electric potential of the L level is applied tothe bias terminal BIAS and the electric potential of the L level isapplied to the selection terminal BE-SW at a time of reset operation,and the electric potential of H level is applied to the bias terminalBIAS and the electric potential of the L level is applied to theselection terminal BE-SW at a time of applying a reverse bias. Forexample, the circuit can be used when the electrode to which a reversebias is applied is the gate electrode of a P-channel transistor.

Thus, using a circuit shown in FIGS. 15A to 15D in this embodiment mode,a reverse bias can be applied to the gate electrode of any transistor inany circuit without changing the electric potentials of other electrodesin the circuit. Further, a forward bias can be applied to both thesignal terminal SIG and the object terminal GATE.

Next, the case where a transistor to which a reverse bias is applied isincluded in the circuits shown in FIGS. 15A to 15D will be describedwith reference to FIGS. 16A to 16H.

FIG. 16A illustrates a circuit including a transistor AC-Tr to which areverse bias is applied is added to the circuit shown in FIG. 15A. Asshown in FIG. 16A, the gate electrode of the transistor AC-Tr may beconnected to the object terminal GATE of the circuit shown in FIG. 15A.FIG. 16B illustrates a circuit in which transistors AC-Tr1 and AC-Tr2 towhich a reverse bias is applied are included in the circuit shown inFIG. 15A. As shown in FIG. 16B, the gate electrodes of the transistorsAC-Tr1 and AC-Tr2 may be connected to the object terminal GATE in thecircuit shown in FIG. 15A.

Here, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may constitute a part ofa circuit having a certain function as the whole as with the transistors53 and 57 in FIGS. 13A to 13C and the transistors 63 and 67 a in FIG.14A to 14C, the circuit of the present invention in which a reverse biasis applied is not dependent on where one of each source electrode andeach drain electrode of the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be N-channeltransistors. Thus, in a period during which an H level is inputted tothe bias terminal BIAS and the L level is inputted to the selectionterminal BE-SW, a signal inputted to a signal terminal SIG is inputtedto the transistor AC-Tr, AC-Tr1, and AC-Tr2, and in a period duringwhich the L level is inputted to the bias terminal BIAS and the H levelis inputted to the selection terminal BE-SW, the electric potentialdependent on the electric potential of the L level of the bias terminalBIAS is applied to the gate electrodes of the transistor AC-Tr, AC-Tr1,and AC-Tr2; thus, a reverse bias can be applied. Further, in a periodduring which the H level is inputted to the bias terminal BIAS and the Hlevel is inputted to the selection terminal BE-SW, an electric potentialdependent on the electric potential of the H level of the bias terminalBIAS can be applied to the gate electrodes of the transistors AC-Tr,AC-Tr1, and AC-Tr2.

Further, FIG. 16C illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied is added to the circuit shown in FIG.15B. As shown in FIG. 16C, the gate electrode of the transistor AC-Trmay be connected to the object terminal GATE of the circuit shown inFIG. 15B.

Further, FIG. 16D illustrates a circuit in which transistors AC-Tr1 andAC-Tr2 to which a reverse bias is applied are included in the circuitshown in FIG. 15B. As shown in FIG. 16D, the gate electrodes of thetransistors AC-Tr1 and AC-Tr2 may be connected to the object terminalGATE in the circuit shown in FIG. 15B. Here, for example, thetransistors AC-Tr, AC-Tr1, and AC-Tr2 may constitute a part of a circuithaving a certain function as the whole as with the transistors 53 and 57in FIGS. 13A to 13C or the transistors 63 and 67 a in FIG. 8A to 8C, thecircuit of the present invention in which a reverse bias is applied isnot dependent on where one of each source electrode and each drainelectrode of the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be N-channeltransistors. Thus, in a period during which an H level is inputted tothe bias terminal BIAS and the H level is inputted to the selectionterminal BE-SW, a signal inputted to a signal terminal SIG is inputtedto the transistor AC-Tr, AC-Tr1, and AC-Tr2, and in a period duringwhich the L level is inputted to the bias terminal BIAS and the L levelis inputted to the selection terminal BE-SW, the electric potentialdependent on the electric potential of the L level of the bias terminalBIAS is applied to the gate electrodes of the transistor AC-Tr, AC-Tr1,and AC-Tr2; thus, a reverse bias can be applied. Further, in a periodduring which the H level is inputted to the bias terminal BIAS and the Llevel is inputted to the selection terminal BE-SW, an electric potentialdependent on the electric potential of the H level of the bias terminalBIAS can be applied to the gate electrodes of the transistors AC-Tr,AC-Tr1, and AC-Tr2.

Further, FIG. 16E illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied is added to the circuit shown in FIG.15C. As shown in FIG. 16E, the gate electrode of the transistor AC-Trmay be connected to the object terminal GATE of the circuit shown inFIG. 15C.

Further, FIG. 16F illustrates a circuit in which transistors AC-Tr1 andAC-Tr2 to which a reverse bias is applied are included in the circuitshown in FIG. 15C. As shown in FIG. 16F, the gate electrodes of thetransistors AC-Tr1 and AC-Tr2 may be connected to the object terminalGATE in the circuit shown in FIG. 15C.

Here, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may constitute a part ofa circuit having a certain function as the whole as with the transistors53 and 57 in FIGS. 13A to 13C and the transistors 63 and 67 a in FIG.14A to 14C, the circuit of the present invention in which a reverse biasis applied is not dependent on where one of each source electrode andeach drain electrode of the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be P-channeltransistors. Thus, in a period during which an L level is inputted tothe bias terminal BIAS and the L level is inputted to the selectionterminal BE-SW, a signal inputted to a signal terminal SIG is inputtedto the transistor AC-Tr, AC-Tr1, and AC-Tr2, in a period during whichthe H level is inputted to the bias terminal BIAS and the H level isinputted to the selection terminal BE-SW, an electric potentialdependent on the electric potential of the H level of the bias terminalBIAS can be applied to the gate electrodes of the transistors AC-Tr,AC-Tr1, and AC-Tr2; thus, a reverse bias can be applied. Further, in aperiod during which the L level is inputted to the bias terminal BIASand the H level is inputted to the selection terminal BE-SW, theelectric potential dependent on the electric potential of the L level ofthe bias terminal BIAS is applied to the gate electrodes of thetransistor AC-Tr, AC-Tr1, and AC-Tr2.

Further, FIG. 16G illustrates a circuit including a transistor AC-Tr towhich a reverse bias is applied is added to the circuit shown in FIG.15D. As shown in FIG. 16G, the gate electrode of the transistor AC-Trmay be connected to the object terminal GATE of the circuit shown inFIG. 15D.

Further, FIG. 16H illustrates a circuit in which transistors AC-Tr1 andAC-Tr2 to which a reverse bias is applied are included in the circuitshown in FIG. 15D. As shown in FIG. 16H, the gate electrodes of thetransistors AC-Tr1 and AC-Tr2 may be connected to the object terminalGATE in the circuit shown in FIG. 15D. Here, the transistors AC-Tr,AC-Tr1, and AC-Tr2 may constitute a part of a circuit having a certainfunction as the whole as with the transistors 53 and 57 in FIGS. 13A to13C ors the transistors 63 and 67 a in FIG. 14A to 14C, the circuit ofthe present invention in which a reverse bias is applied is notdependent on where one of each source electrode and each drain electrodeof the transistors AC-Tr, AC-Tr1, and AC-Tr2.

Further, the transistors AC-Tr, AC-Tr1, and AC-Tr2 may be P-channeltransistors. Thus, in a period during which an L level is inputted tothe bias terminal BIAS and the H level is inputted to the selectionterminal BE-SW, a signal inputted to a signal terminal SIG is inputtedto the transistor AC-Tr, AC-Tr1, and AC-Tr2, in a period during whichthe H level is inputted to the bias terminal BIAS and the L level isinputted to the selection terminal BE-SW, an electric potentialdependent on the electric potential of the H level of the bias terminalBIAS can be applied to the gate electrodes of the transistors AC-Tr,AC-Tr1, and AC-Tr2; thus, a reverse bias can be applied. Further, in aperiod during which the L level is inputted to the bias terminal BIASand the L level is inputted to the selection terminal BE-SW, theelectric potential dependent on the electric potential of the L level ofthe bias terminal BIAS is applied to the gate electrodes of thetransistor AC-Tr, AC-Tr1, and AC-Tr2.

Note that this embodiment mode can be freely combined with any one ofthe other embodiment modes.

Embodiment Mode 4

In this embodiment mode, description will be given of a top view and across-sectional view of the case of forming a shift register circuit ofthe invention by fabricating an element on a substrate with reference tothe drawing. FIG. 17 illustrates an example of forming circuits 10 as ashift register circuit of the present invention using a top gatetransistor as a transistor. In FIG. 17, only the circuit 10 at a kthstage (shown as 10 k) and the circuit 10 of a (k+1)th stage (shown as 10k+1) are illustrated for description; however, the present invention isnot limited thereto, and the circuits 10 may have any number of stages.Further, transistors 11, 12, 13, 15, 16, and 17, a capacitor 10 element14, and a terminal P in FIG. 17 may correspond to the transistors 11,12, 13, 15, 16, and 17, the capacitor element 14, and the terminal P inFIG. 1B respectively. The electrode SR and the output terminal L whichare arranged outside the circuits 10 in FIGS. 1A to 1C are arrangedinside the circuits 10 in FIG. 17 in order to reduce the layout area.Note that in the top view referred in this embodiment mode, a regionindicated by a broken line is a region where there is another layer in alayer above the region.

In FIG. 17, a power supply line Vss, a first clock signal line CLK1, asecond clock signal line CLK2 are each formed from a wiring layer, andthey may be provided in substantially parallel to the direction wherethe circuits 10 extend (shown as 10 ext). Thus, in the case of providinga plurality of circuits 10, the length of leading the wiring isincreased and wiring resistance is increased accordingly, and thus,malfunctions and increase in power consumption due to voltage drop ofthe power supply line can be prevented. Further, malfunctions caused bydistortion of a signal waveform, reduction in the range of voltage wherethe circuit operates normally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond clock signal line CLK2 may be provided outside elements formingthe circuit 10. Further, the power supply line Vss may be providedopposite to the first clock signal line CLK1 and the second clock signalline CLK2. Thus, the power supply line Vss can be prevented fromcrossing the first clock signal line CLK1 and the second clock signalline CLK2; thus, the power supply line can be prevented from beingaffected by noise from the, and malfunctions can be reduced.

Here, in this embodiment mode, a region where an active layer regionoverlaps with a gate electrode region in a transistor is also referredto as a channel region. Further, one of the regions in the active layerof the transistor, which are separated by the channel region transistoris referred to as “one of a source electrode and a drain electrode” andthe other of the regions separated by the channel region is referred toas “the other of the source electrode and the drain electrode”. Further,the direction of a tangential line of the boundaries between the one orthe other of the source electrode and the drain electrode of thetransistor and the channel region of the transistor is referred to as “achannel width direction”. Further, the direction perpendicular to thechannel width direction is referred to as a “channel length direction”.For example, in a transistor of this embodiment mode, when theboundaries between one or the other of a source electrode and a drainelectrode of the transistor and a channel region of the transistor arecurved, the channel width direction and the channel length direction mayvary depending on points in the boundaries.

In FIG. 17, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially perpendicular. With this structure, the areaof a substrate occupied by the transistors 11 and 12 can be minimized,and circuit scale can be reduced.

Further, the channel length directions of the transistors 13 and 16(shown as Ch1) may be substantially parallel to each other; they mayshare either one source electrode or one drain electrode. Thus, the areaof a substrate which is occupied by the transistors 13 and 16 can beminimized and circuit scale can be reduced. Further, channel lengthdirections of the transistors 15 and 17 (shown as Ch2) may besubstantially parallel to each other, and they may share either onesource electrode or one drain electrode. Thus, the area of a substrateoccupied by the transistors 15 and 17 can be minimized, and circuitscale can be reduced.

Further, one of the electrodes of the capacitor element 14, the terminalP, may be formed from a gate electrode, and the other of the electrodes,an electrode connected to the output terminal L, may be formed from awiring layer. Further, in the case where the transistor is an n-channeltransistor, the active layer of the transistor and the wiring layerconnected to the output terminal L may be connected to each other andthe gate electrode constituting the terminal P may be interposed betweenthe active layer and the wiring layer to form the capacitor element 14.When the terminal P is formed from the gate electrode, when the electricpotential of the terminal P becomes high, carriers are generated in theactive layer connected to the output terminal L. Therefore, thecapacitance value of the capacitor element 14 formed from the activelayer and the gate electrode can be increased.

Next, a cross-sectional view taken along line A-A′ in FIG. 17 in thecase of using a thin film transistor as a transistor will be describedwith reference to FIG. 18. A structure shown in FIG. 18 is provided witha substrate 100, a base film 101, an active layer 102, an insulatingfilm 103, gate electrodes 104 and 105, an interlayer film 106, and awiring layer 108. Further, the structure shown in FIG. 18 is providedwith contacts 107 a and 107 b which connect the wiring layer 108 and theactive layer 102, and a contact 107 c which connects the wiring layer108 and the gate electrode 104. The structure shown in FIG. 18 will bedescribed step by step.

First, the substrate 100 may be a glass substrate formed from bariumborosilicate glass, aluminoborosilicate glass, or the like; a quartzsubstrate, a silicon substrate, a metal substrate, a stainless-steelsubstrate, or a plastic substrate. Further, the substrate 100 may bepolished by CMP or the like to planarize a surface of the substrate 100.

Next, a base film 101 may be formed over the substrate 100. The basefilm 101 may be formed from a single layer of nitride aluminum (AlN),silicon oxide (SiO₂), silicon oxynitride (SiOxNy), or the like or alaminate thereof by a known method such as CVD, plasma CVD, sputtering,or spin coating. Note the base film 101 has an effect of blockingimpurities such as contaminants from the substrate 100. When the basefilm 101 is not formed, the manufacturing process is simplified, andcost can be reduced.

Next, the active layer 102 may be formed over the substrate 100 or thebase film 101. Here, the active layer 102 may be formed of polysilicon(p-Si). The active layer 102 may be selectively formed to a desiredshape by photolithography, a droplet discharge method, a printing methodor the like.

Next, an insulating film 103 may be formed over the substrate 100, thebase film 101, or the active layer 102. Here, the insulating film 103may be formed of silicon oxide (SiO₂) or silicon oxynitride (SiOxNy).

Next, the gate electrodes 104 and 105 may be formed over the substrate100, the base film 101, the active layer 102, or the insulating film103. Here, the gate electrodes 104 and 105 may be selectively formedfrom different kinds of metals to a desired shape by photolithography, adroplet discharge method, a printing method or the like. Thus, in thecase where the gate electrodes 104 and 105 are processed by etchingusing photolithography or the like, the etching is performed so thatetch selectivity can be obtained between the gate electrodes 104 and105; thus, the gate electrode 104 and the gate electrode 105 can beformed to have different areas without modifying a photomask. Thus, inthe case where the conductivity of the active layer 102 is controlled byadding charged particles into the active layer 102, an LDD region can beformed in the active layer 102 without modifying a photomask.Accordingly, a transistor in which high electric field is hardly appliedand deterioration due to hot carriers is small can be manufactured.

Next, the interlayer film 106 may be formed over the substrate 100, thebase film 101, the active layer 102, the insulating film 103, or thegate electrodes 104 and 105. Here, the interlayer film 106 can be formedfrom an insulating material such as silicon oxide, silicone nitride,silicon oxynitride, aluminum oxide, aluminum nitride, aluminumoxynitride or other inorganic insulating materials; acrylic acid ormethacrylic acid, or a derivative thereof; a heat resistant polymer suchas polyimide, aromatic polyamide, polybenzimidazole; or a siloxaneresin. Note that the siloxane resin refers to resin having a bond ofSi—O—Si. The skeletal structure of siloxane is formed from a bond ofsilicon (Si) and oxygen (O). An organic group (for example, an alkylgroup or aromatic hydrocarbon) containing at least hydrogen is used asthe substituent. A fluoro group may also be used as the substituent.Alternatively, an organic group at least containing hydrogen and afluoro group may be used as the substituent. When the interlayer film isformed from a photosensitive or a non photosensitive material such asacrylic or polyimide, the interlayer film has curved sides in which thecurvature radius is changed continuously, and a thin film thereon can beformed without disconnection, which is preferable. Further, theinterlayer film 106 may be formed to a desired shape byphotolithography, a droplet discharge method, a printing method, or thelike. Here, the interlayer film 106 may be processed by etching so thatetching ends before the gate electrodes 104 and 105 are etched as withthe contact 107 c while the insulating film 103 is also processed aswith the contacts 107 a and 107 b. Then, the wiring layer 108 can beformed so that the active layer 102 is connected to the gate electrodes104 and 105.

The wiring layer 108 may be formed over the substrate 100, the base film101, active layer 102, the insulating film 103, the gate electrodes 104and 105, or the interlayer film 106. Here, a composition containingparticles of metal such as Ag (silver), Au (gold), Cu (copper), W(tungsten), or Al (aluminum) as main components can be used as amaterial for forming the wiring layer 108. Further, a light-transmittingmaterial such as indium tin oxide (ITO), ITSO containing indium tinoxide and silicon oxide, organoindium, organotin, zinc oxide, titaniumnitride may be combined. Further, the wiring layer 108 may be formed toa desired shape by photolithography, a droplet discharge method, aprinting method, or the like.

Next, description will be given of a top view of the circuits 10 of thecase where the shapes of the transistors 13 and 17 are devised tomaintaining the electric potential of the electrode SR at H levelthereby fixing the electric potentials of the terminal P and the outputterminal L with reference to FIG. 19. The circuit 10 shown in the topview of FIG. 19 is provided with transistors 11, 12, 13, 15, 16, and 17,and a capacitor element 14 as in FIG. 17, and connections are alsosimilar; however, the areas of channel regions of the transistors 13 and17 are different. Thus, when the average of the of areas of the gateelectrodes in the transistors 13 and 17 is made larger than the area ofthe gate electrode in the transistor 12 of the circuit 10, the value ofparasitic capacitance associated with the electrode SR can be madeLarger; thus, the electric potential of the electrode SR can bemaintained at H level even after a reset operation, which is preferable.Further, as shown in FIG. 19, the electrode SR may be formed to becurved in the circuit 10 so as not to make the shape linear. Thus, thelength of leading the electrode SR can be made longer than the pitchbetween the circuit 10 of the kth stage and the circuit 10 of the(k+1)th stage. Accordingly, the value of parasitic capacitanceassociated with the electrode SR can be increased, so that the electricpotential of the electrode SR can be maintained at H level even after areset operation, which is preferable.

Next, description will be given of a top view of the case where crosscapacitance of the clock signal line and the output terminal L iseliminated so that the output terminal L is not affected by change inthe electric potential of the clock signal line as possible withreference to FIG. 20. The circuit 10 shown in the top view of FIG. 20 isprovided with transistors 11, 12, 13, 15, 16, and 17, a capacitorelement 14, a terminal P, an electrode SR, and an output terminal L asin FIG. 17 and FIG. 19, and the connections are also similar; however,the arrangement of the first clock signal line CLK1, the second clocksignal line CLK2, and the transistors 11 and 12 is different form FIG.17 and FIG. 19.

In FIG. 20, the power supply line Vss, the first clock signal line CLK1,and the second clock signal line CLK2 are formed from a wiring layer,and may be provided in substantially parallel to the direction where thecircuits 10 extend (shown as 10 ext). Thus, in the case of providing aplurality of circuits 10, the length of leading the wiring is increasedand wiring resistance is increased accordingly, and thus, malfunctionsand increase in power consumption due to voltage drop of the powersupply line can be prevented. Further, malfunctions caused by distortionof a signal waveform, reduction in the range of voltage where thecircuit operates normally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond clock signal line CLK2 may be provided outside elements formingthe circuit 10. Further, the power supply line Vss, and the first clocksignal line CLK1 and the second clock signal line CLK2 may be providedon the same side which is opposite to the side where the output terminalL is provided, with respect to the first transistor, the thirdtransistor, the second transistor, and the fourth transistor. Thus, theoutput terminal L can be prevented from crossing the first clock signalline CLK1 and the second clock signal line CLK2; thus, the power supplyline can be prevented from being affected by noise from the clock signalline, and malfunctions can be reduced.

Further, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially parallel. With this structure, the area of asubstrate occupied by the transistors 11 and 12 can be minimized, andcircuit scale can be reduced and generation of a region where the outputterminal L crosses the first clock signal line CLK1 and the second clocksignal line CLK2 can be prevented as well.

Next, description will be given of a top view of the case of a shiftregister circuit of the present invention of the case where a bottomgate transistor is used as a transistor and an active layer is processedinto a desired shape using a wiring layer as a mask with reference toFIG. 21. In FIG. 21, only the circuit 10 at a kth stage (shown as 10 k)and the circuit 10 of a (k+1)th stage (shown as 10 k+1) are illustratedfor description; however, the present invention is not limited thereto,and the circuits 10 may have any number of stages. Further, transistors11, 12, 13, 15, 16, and 17, a capacitor element 14, and a terminal P inFIG. 21 may correspond to the transistors 11, 12, 13, 15, 16, and 17,the capacitor element 14, and the terminal P in FIG. 1B respectively.The electrode SR and the output terminal L which are arranged outsidethe circuits 10 in FIGS. 1A to 1C are arranged inside the circuits 10 inFIG. 21 in order to reduce the layout area. Note that in the top viewreferred in this embodiment mode, a region indicated by a broken line isa region where there is another layer in a layer above the region.

Next, cross-sectional views taken along lines a-a′ and b-b′ in FIG. 21of the case of using a thin film transistor as a transistor will bedescribed with reference to FIGS. 22A and 22B. A structure shown inFIGS. 22A and 22B is provided with a substrate 110, a base film 111, afirst wiring layer 112, an insulating film 113, active layers 114 and115, a second wiring layer 116, an interlayer film 117, and a thirdwiring layer 119. Further, the structure shown in FIGS. 22A and 22B isprovided with a contact 118 a which connect the third wiring layer 119and the second wiring layer 116, and a contact 118 b which connects thethird wiring layer 119 and the first wiring layer 112. The structureshown in FIGS. 22A and 22B will be described step by step.

First, the substrate 110 may be a glass substrate formed from bariumborosilicate glass, aluminoborosilicate glass, or the like; a quartzsubstrate, a silicon substrate, a metal substrate, a stainless-steelsubstrate, or a plastic substrate. Further, the substrate 110 may bepolished by CMP or the like to planarize a surface of the substrate 110.

Next, a base film 111 may be formed over the substrate 110. The basefilm 111 may be formed from a single layer of nitride aluminum (AlN),silicon oxide (SiO₂), silicon oxynitride (SiOxNy), or the like or alaminate thereof by a known method such as CVD, plasma CVD, sputtering,or spin coating. Note the base film 111 has an effect of blockingimpurities such as contaminants from the substrate 110. When the basefilm 101 is not formed, the manufacturing process is simplified, andcost can be reduced.

Next, the first wiring layer 112 may be formed over the substrate 110 orthe base film 111. Here, the first wiring layer 112 may be processedinto a desired shape by photolithography, a droplet discharge method, aprinting method or the like.

Next, an insulating film 113 may be formed over the substrate 110, thebase film 101, or the first wiring layer 112. Here, the insulating film113 may be formed of silicon oxide (SiO₂) or silicon oxynitride(SiOxNy).

Next, the active layers 114 and 115 may be formed over the substrate110, the base film 111, the first wiring layer 112, or the insulatingfilm 113. Here, the active layers 114 and 115 may be formed of amorphoussilicon (a-Si), and the active layers 114 and 115 may be continuouslyformed in the same film formation apparatus. The active layer 115 mayhave higher conductivity compared to the active layer 114. Note that aregion in the vicinity of the interface between the channel region,specifically the active layer 114, and the insulating film 113 may bedenser than the other region of the active layer 114. Thus,deterioration of the transistor can be suppressed, and film formationrate of the active layer 114 can be speeded; thus, throughput improve isimproved.

The second wiring layer 116 may be formed over the substrate 110, thebase film 111, the first wiring layer 112, the insulating film 113, orthe active layers 114 and 115. Here, a composition containing particlesof metal such as Ag (silver), Au (gold), Cu 10 (copper), W (tungsten),or Al (aluminum) as main components can be used as a material forforming the second wiring layer 116. Further, a light-transmittingmaterial such as indium tin oxide (ITO), ITSO containing indium tinoxide and silicon oxide, organoindium, organotin, zinc oxide, titaniumnitride may be combined. Further, the second wiring layer 116 may beprocessed into a desired shape by photolithography, a droplet dischargemethod, a printing method, or the like.

Next, the interlayer film 117 may be formed over the substrate 110, thebase film 111, the first wiring layer 112, the insulating film 113, orthe active layers 114 and 115, or the second wiring layer 116. Here, theinterlayer film 117 can be formed from an insulating material such assilicon oxide, silicone nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or other inorganic insulatingmaterials; acrylic acid or methacrylic acid, or a derivative thereof; aheat resistant polymer such as polyimide, aromatic polyamide,polybenzimidazole; or a siloxane resin. Further, the interlayer film 117may be processed into a desired shape by photolithography, a dropletdischarge method, a printing method, or the like. When the interlayerfilm is formed from a photosensitive or a non photosensitive materialsuch as acrylic or polyimide, the interlayer film has curved sides inwhich the curvature radius is changed continuously, and a thin filmthereon can be formed without disconnection, which is preferable.Further, the interlayer film 117 may be processed into a desired shapeby photolithography, a droplet discharge method, a printing method, orthe like. Here, the interlayer film 117 may be processed so that etchingends before the wiring layer 116 is etched as with the contact 118 awhile the insulating film 113 is also processed as with the contact 118b. Then, the second wiring layer 116 can be formed so that the secondwiring layer 116 is connected to the first wiring layer 112.

The third wiring layer 119 may be formed over the substrate 110, thebase film 111, the first wiring layer 112, the insulating film 113, theactive layers 114 and 115, the second wiring layer 116, or theinterlayer film 117. Here, a composition containing particles of metalsuch as Ag (silver), Au (gold), Cu (copper), W (tungsten), or Al(aluminum) as main components can be used as a material for forming thethird wiring layer 119. Further, a light-transmitting material such asindium tin oxide (ITO), ITSO containing indium tin oxide and siliconoxide, organoindium, organotin, zinc oxide, titanium nitride may becombined. Further, the third wiring layer 119 may be processed into adesired shape by photolithography, a droplet discharge method, aprinting method, or the like.

Note that, in FIG. 22A, Reference numeral Ctft17 denotes a parasiticcapacitance element of the transistor 17, Cclk1 denotes a parasiticcapacitance element of the output terminal L and the first clock signalline CLK1, and Cclk2 denotes a parasitic capacitance element of theoutput terminal L and the second clock signal line CLK2 respectively.Reference numeral x in FIG. 22A denotes a width of the first wiringlayer over which the active layer exist in the parasitic capacitanceelement Ctft17. Reference numeral y denotes a distance between the upperend of the first wiring layer and the lower end of the second wiringlayer in the parasitic capacitance elements Cclk1 and Cclk2.

Here, in FIG. 21, since the active layers are formed using the secondwiring layer as a mask, they are formed into a shape in accordance withthe second wiring layer. Thereupon, the active layers may be formed tohave a shape such as to surround the second wiring layer. Thus, coverageof the third wiring layer laid over the second wiring layer is improved,and disconnection of the third wiring layer can be prevented. That isbecause, for example, when a shape of the perimeter of the active layerand a shape of the perimeter of the second wiring layer is the same oralmost the same, or when the second wiring layer surrounds the activelayer, the taper angle of the interlayer film on the second wiring layeris sharper compared with the case where the active layer is formed tohave a shape such as to surround the second wiring layer.

Further, in FIG. 21, a power supply line Vss, a first clock signal lineCLK1, a second clock signal line CLK2 are each formed from a wiringlayer and the active layer, and they may be provided in substantiallyparallel to the direction where the circuits 10 extend (shown as 10ext). Thus, in the case of providing a plurality of circuits 10, thelength of leading the wiring is increased and wiring resistance isincreased accordingly, and thus, malfunctions and increase in powerconsumption due to voltage drop of the power supply line can beprevented. Further, malfunctions caused by distortion of a signalwaveform, reduction in the range of voltage where the circuit operatesnormally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond 10 clock signal line CLK2 may be provided outside elementsforming the circuit 10. Further, the power supply line Vss may beprovided opposite to the first clock signal line CLK1 and the secondclock signal line CLK2. Thus, the power supply line Vss can be preventedfrom crossing the first clock signal line CLK1 and the second clocksignal line CLK2; thus, the power supply line can be prevented frombeing affected by noise from the clock signal line, and malfunctions canbe reduced.

In FIG. 21, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially perpendicular. With this structure, the areaof a substrate occupied by the transistors 11 and 12 can be minimized,and circuit scale can be reduced. Further, the channel length directionsof the transistors 13 and 16 (shown as Ch1) may be substantiallyparallel to each other; they may share either one source electrode orone drain electrode. Thus, the area of a substrate which is occupied bythe transistors 13 and 16 can be minimized and circuit scale can bereduced.

Further, channel length directions of the transistors 15 and 17 (shownas Ch2) may be substantially parallel to each other, and they may shareeither one source electrode or one drain electrode. Thus, the area of asubstrate occupied by the transistors 15 and 17 can be minimized, andcircuit scale can be reduced.

Next, description will be given of a top view of the circuits 10 of thecase where the shapes of the transistors 13 and 17 are devised tomaintaining the electric potential of the electrode SR at H levelthereby fixing the electric potentials of the terminal P and the outputterminal L with reference to FIG. 23. The circuit 10 shown in the topview of FIG. 23 is provided with transistors 11, 12, 13, 15, 16, and 17,a capacitor element 14, the terminal P, the electrode SR, and the outputterminal L as in FIG. 21, and connections are also similar; however, theshapes of the first wiring layer of the transistors 13 and 17 aredifferent. Thus, when the average of the of areas of the first wiringlayer in the transistors 13 and 17 is made larger than the area of thefirst wiring layer in the transistor 12 of the circuit 10, the value ofparasitic capacitance associated with the electrode SR can be madelarger; thus, the electric potential of the electrode SR can bemaintained at H level even after a reset operation, which is preferable.

Further, as shown in FIG. 23, the electrode SR may be formed to becurved in the circuit 10 so as not to make the shape linear. Thus, thelength of leading the electrode SR can be made longer than the pitchbetween the circuit 10 of the kth stage (shown as 10 k) and the circuit10 of the (k+1)th stage (shown as 10 k+1). Accordingly, the value ofparasitic capacitance associated with the electrode SR can be increased,so that the electric potential of the electrode SR can be maintained atH level even after a reset operation, which is preferable. Further, thecircuits 10 shown in the top view of FIG. 23 have a different structureof the region where the output terminal L crosses the clock signal linefrom one in FIG. 21. In the circuits 10 shown in FIG. 23, in the regionwhere the output terminal L crosses the clock signal line, the outputterminal L is formed with the third wiring layer, and the clock signalline can be formed with the second wiring layer and the active layer.

Next, cross-sectional views taken along lines a-a′ and b-b′ in FIG. 23of the case of using a thin film transistor as a transistor will bedescribed with reference to FIGS. 24A and 24B. A structure shown inFIGS. 24A and 24B is provided with a substrate 110, a base film 111, afirst wiring layer 112, an insulating film 113, active layers 114 and115, a second wiring layer 116, an interlayer film 117, and a thirdwiring layer 119 as the structure shown in FIGS. 22A and 22B. Further,the structure shown in FIGS. 24A and 24B is provided with a contact 118a which connect the third wiring layer 119 and the second wiring layer116, and a contact 118 b which connects the third wiring layer 119 andthe first wiring layer 112.

Note that, in FIG. 24A, Reference numeral Ctft17 denotes a parasiticcapacitance element of the transistor 17, Cclk1 denotes a parasiticcapacitance element of the output terminal L and the first clock signalline CLK1, and Cclk2 denotes a parasitic capacitance element of theoutput terminal L and the second clock signal line CLK2 respectively.Reference numeral x in FIG. 24A denotes a width of the first wiringlayer over which the active layer exist in the parasitic capacitanceelement Ctft17. Reference numeral y denotes a distance between the upperend of the first wiring layer and the lower end of the second wiringlayer in the parasitic capacitance elements Cclk1 and Cclk2.

Here, the capacitance value of the parasitic capacitance element Ctft17becomes larger as x is larger. Meanwhile, the capacitance values of theparasitic capacitance elements Cclk1 and Cclk2 become smaller as y islarger. When the capacitance value of the parasitic capacitance elementCtft17 is increased by making x larger as shown in FIG. 24A, parasiticcapacitance value associated with the electrode SR can be increased;thus, the electric potential of the electrode SR can be maintained at Hlevel sufficiently. Further, when the capacitance values of theparasitic capacitance elements Cclk1 and Cclk2 is reduced by making ylarger as in FIG. 24B, change in the electric potential of the outputterminal L due to change in the electric potentials of the first clocksignal line CLK1 and the second clock signal line CLK2 through theparasitic capacitance elements Cclk1 and Cclk2, can be reduced.Thereupon, the first clock signal line CLK1 and the second clock signalline CLK2 may be formed with the first wiring layer.

Next, description will be given of a top view of the case where crosscapacitance of the clock signal line and the output terminal L iseliminated so that the output terminal L is not affected by change inthe electric potential of the clock signal line as possible withreference to FIG. 25. The circuit 10 shown in the top view of FIG. 25 isprovided with transistors 11, 12, 13, 15, 16, and 17, a capacitorelement 14, a terminal P, an electrode SR, and an output terminal Las inFIG. 21 and FIG. 23, and the connections are also similar; however, thearrangement of the first clock signal line CLK1, the second clock signalline CLK2, and the transistors 11 and 12 is different form FIG. 21 andFIG. 23.

In FIG. 25, the power supply line Vss, the first clock signal line CLK1,and the second clock signal line CLK2 are formed from the second wiringlayer and the active layer, and may be provided in substantiallyparallel to the direction where the circuits 10 extend. Thus, in thecase of providing a plurality of circuits 10, the length of leading thewiring is increased and wiring resistance is increased accordingly, andthus, malfunctions and increase in power consumption due to voltage dropof the power supply line can be prevented. Further, malfunctions causedby distortion of a signal waveform, reduction in the range of voltagewhere the circuit operates normally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond clock signal line CLK2 may be provided outside elements formingthe circuit 10. Further, the power supply line Vss, and the first clocksignal line CLK1 and the second clock signal line CLK2 may be providedon the same which is opposite to the side where the output terminal L isprovided, with respect to the first transistor, the third transistor,the second transistor, and the fourth transistor. Thus, the outputterminal L can be prevented from crossing the first clock signal lineCLK1 and the second clock signal line CLK2; thus, the power supply linecan be prevented from being affected by noise from the clock signalline, and malfunctions can be reduced.

Further, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially parallel. With this structure, the area of asubstrate occupied by the transistors 11 and 12 can be minimized, andcircuit scale can be reduced and generation of a region where the outputterminal L crosses the first clock signal line CLK1 and the second clocksignal line CLK2 can be prevented as well.

Next, description will be given of a top view of the case of a shiftregister circuit of the present invention of the case where a bottomgate transistor is used as a transistor and an active layer and a wiringlayer are separately processed into desired shapes with reference toFIG. 26. In FIG. 26, only the circuit 10 at a kth stage (shown as 10 k)and the circuit 10 of a (k+1)th stage (shown as 10 k+1) are illustratedfor description; however, the present invention is not limited thereto,and the circuits 10 may have any number of stages. Further, transistors11, 12, 13, 15, 16, and 17, a capacitor element 14, and a terminal P inFIG. 26 may correspond to the transistors 11, 12, 13, 15, 16, and 17,the capacitor element 14, and the terminal P in FIG. 1B respectively.The electrode SR and the output terminal L which are arranged outsidethe circuits 10 in FIGS. 1A to 1C are arranged inside the circuits 10 inFIG. 26 in order to reduce the layout area. Note that in the top viewreferred in this embodiment mode, a region indicated by a broken line isa region where there is another layer in a layer above the region.

Next, cross-sectional views taken along lines a-a′ and b-b′ in FIG. 26of the case of using a thin film transistor as a transistor will bedescribed with reference to FIGS. 27A and 27B. A structure shown inFIGS. 27A and 27B is provided with a substrate 120, a base film 121, afirst wiring layer 122, an insulating film 123, active layers 124 and125, a second wiring layer 126, an interlayer film 127, and a thirdwiring layer 129. Further, the structure shown in FIGS. 27A and 27B isprovided with a contact 128 a which connect the third wiring layer 129and the second wiring layer 126, and a contact 128 b which connects thethird wiring layer 129 and the first wiring layer 122. The structureshown in FIGS. 27A and 27B will be described step by step.

First, the substrate 120 may be a glass substrate formed from bariumborosilicate glass, aluminoborosilicate glass, or the like; a quartzsubstrate, a silicon substrate, a metal substrate, a stainless-steelsubstrate, or a plastic substrate. Further, the substrate 120 may bepolished by CMP or the like to planarize a surface of the substrate 120.

Next, a base film 121 may be formed over the substrate 120. The basefilm 121 may be formed from a single layer of nitride aluminum (AlN),silicon oxide (SiO₂), silicon oxynitride (SiOxNy), or the like or alaminate thereof by a known method such as CVD, plasma CVD, sputtering,or spin coating. Note the base film 121 has an effect of blockingimpurities such as contaminants from the substrate 120. When the basefilm 121 is not formed, the manufacturing process is simplified, andcost can be reduced.

Next, a first wiring layer 122 may be formed over the substrate 120 orthe base film 121. Here, the first wiring layer 122 may be processedinto a desired shape by photolithography, a droplet discharge method, aprinting method or the like.

Next, an insulating film 123 may be formed over the substrate 120, thebase film 121, or the first wiring layer 122. Here, the insulating film123 may be formed of silicon oxide (SiO₂) or silicon oxynitride(SiOxNy).

Next, active layers 124 and 125 may be formed over the substrate 120,the base film 121, the first wiring layer 122, or the insulating film123. Here, the active layers 124 and 125 may be formed of amorphoussilicon (a-Si), and the active layers 124 and 125 may be continuouslyformed in the same film formation apparatus. The active layer 125 mayhave higher conductivity compared to the active layer 124. Note that aregion in the vicinity of the interface between the channel region,specifically the active layer 124, and the insulating film 123 may bedenser than the other region of the active layer 124. Thus,deterioration of the transistor can be suppressed, and film formationrate of the active layer 124 can be speeded; thus, throughput improve isimproved.

A second wiring layer 126 may be formed over the substrate 120, the basefilm 121, the first wiring layer 122, the insulating film 123, or theactive layers 124 and 125. Here, a composition containing particles ofmetal such as Ag (silver), Au (gold), Cu (copper), W (tungsten), or Al(aluminum) as main components can be used as a material for forming thesecond wiring layer 126. Further, a light-transmitting material such asindium tin oxide (ITO), ITSO containing indium tin oxide and siliconoxide, organoindium, organotin, zinc oxide, titanium nitride may becombined. Further, the second wiring layer 126 may be processed into adesired shape by photolithography, a droplet discharge method, aprinting method, or the like.

Next, an interlayer film 127 may be formed over the substrate 120, thebase film 121, the first wiring layer 122, the insulating film 123, orthe active layers 124 and 125, or the second wiring layer 126. Here, theinterlayer film 127 can be formed from an insulating material such assilicon oxide, silicone nitride, silicon oxynitride, aluminum oxide,aluminum nitride, aluminum oxynitride or other inorganic insulatingmaterials; acrylic acid or methacrylic acid, or a derivative thereof; aheat resistant polymer such as polyimide, aromatic polyamide,polybenzimidazole; or a siloxane resin. Further, the interlayer film 127may be processed into a desired shape by photolithography, a dropletdischarge method, a printing method, or the like. When the interlayerfilm is formed from a photosensitive or a non photosensitive materialsuch as acrylic or polyimide, the interlayer film has curved sides inwhich the curvature radius is changed continuously, and a thin filmthereon can be formed without disconnection, which is preferable.Further, the interlayer film 127 may be processed into a desired shapeby photolithography, a droplet discharge method, a printing method, orthe like. Here, the interlayer film 127 may be processed so that etchingends before the wiring layer 126 is etched as with the contact 128 awhile the insulating film 123 is also processed as with the contact 128b. Then, the second wiring layer 126 can be formed so that the secondwiring layer 126 is connected to the first wiring layer 122.

A third wiring layer 129 may be formed over the substrate 120, the basefilm 121, the first wiring layer 122, the insulating film 123, theactive layers 124 and 125, the second wiring layer 126, or theinterlayer film 127. Here, a composition containing particles of metalsuch as Ag (silver), Au (gold), Cu (copper), W (tungsten), or Al(aluminum) as main components can be used as a material for forming thethird wiring layer 129. Further, a light-transmitting material such asindium tin oxide (ITO), ITSO containing indium tin oxide and siliconoxide, organoindium, organotin, zinc oxide, titanium nitride may becombined. Further, the third wiring layer 129 may be processed into adesired shape by photolithography, a droplet discharge method, aprinting method, or the like.

Note that, in FIG. 27A, Reference numeral Ctft17 denotes a parasiticcapacitance element of the transistor 17, Cclk1 denotes a parasiticcapacitance element of the output terminal L and the first clock signalline CLK1, and Cclk2 denotes a parasitic capacitance element of theoutput terminal L and the second clock signal line CLK2 respectively.Reference numeral x in FIG. 27A denotes a width of the first wiringlayer over which the active layer exist in the parasitic capacitanceelement Ctft17. Reference numeral y denotes a distance between the upperend of the first wiring layer and the lower end of the second wiringlayer in the parasitic capacitance elements Cclk1 and Cclk2. Here inorder to increase y, in a region where the output terminal L crosses thefirst clock signal line CLK1 and the second clock signal line CLK2 in across-section taken along line b-b′, active layers 124 and 125 may beformed.

Since the active layer and the second wiring layer are separately formedusing different masks in FIG. 26, a region provided with an active layeris not necessarily formed in the second wiring layer other than atransistor area therein. Further, as with the region where the outputterminal L crosses the first clock signal line CLK1 and the second clocksignal line CLK2 as in FIG. 26, an active layer may be formed in secondwiring layer other than the transistor area.

Further, in FIG. 26, a power supply line Vss, a first clock signal lineCLK1, a second clock signal line CLK2 are each formed from a wiringlayer and the active layer, and they may be provided in substantiallyparallel to the direction where the circuits 10 extend (shown as 10ext). Thus, in the case of providing a plurality of circuits 10, thelength of leading the wiring is increased and wiring resistance isincreased accordingly, and thus, malfunctions and increase in powerconsumption due to voltage drop of the power supply line can beprevented. Further, malfunctions caused by distortion of a signalwaveform, reduction in the range of voltage where the circuit operatesnormally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond clock signal line CLK2 may be provided outside elements formingthe circuit 10. Further, the power supply line Vss may be providedopposite to the first clock signal line CLK1 and the second clock signalline CLK2. Thus, the power supply line Vss can be prevented fromcrossing the first clock signal line CLK1 and the second clock signalline CLK2; thus, the power supply line can be prevented from beingaffected by noise from the clock signal line, and malfunctions can bereduced.

In FIG. 26, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially perpendicular. With this structure, the areaof a substrate occupied by the transistors 11 and 12 can be minimized,and circuit scale can be reduced.

Further, the channel length directions of the transistors 13 and 16(shown as Ch1) may be substantially parallel to each other; they mayshare either one source electrode or one drain electrode. Thus, the areaof a substrate which is occupied by the transistors 13 and 16 can beminimized and circuit scale can be reduced. Further, channel lengthdirections of the transistors 15 and 17 (shown as Ch2) may besubstantially parallel to each other, and they may share either onesource electrode or one drain electrode. Thus, the area of a substrateoccupied by the transistors 15 and 17 can be minimized, and circuitscale can be reduced.

Next, description will be given of a top view of the circuits 10 of thecase where the shapes of the transistors 13 and 17 are devised tomaintaining the electric potential of the electrode SR at H levelthereby fixing the electric potentials of the terminal P and the outputterminal L with reference to FIG. 28. The circuit 10 shown in the topview of FIG. 28 is provided with transistors 11, 12, 13, 15, 16, and 17,a capacitor element 14, the terminal P, the electrode SR, and the outputterminal Las in FIG. 26, and connections are also similar; however, theshapes of the first wiring layer of the transistors 13 and 17 aredifferent. Thus, when the average of the of areas of the first wiringlayer in the transistors 13 and 17 is made larger than the area of thefirst wiring layer in the transistor 12 of the circuit 10, the value ofparasitic capacitance associated with the electrode SR can be madelarger; thus, the electric potential of the electrode SR can bemaintained at H level even after a reset operation, which is preferable.

Further, as shown in FIG. 28, the electrode SR may be formed to becurved in the circuit 10 so as not to make the shape linear. Thus, thelength of leading the electrode SR can be made longer than the pitchbetween the circuit 10 of the kth stage (shown as 10 k) and the circuit10 of the (k+1)th stage (shown as 10 k+1). Accordingly, the value ofparasitic capacitance associated with the electrode SR can be increased,so that the electric potential of the electrode SR can be maintained atH level even after a reset operation, which is preferable.

Further, the circuits 10 shown in the top view of FIG. 28 have adifferent structure of the region where the output terminal L crossesthe clock signal line from one in FIG. 26. In the circuits 10 shown inFIG. 28, in the region where the output terminal L crosses the clocksignal line, the output terminal L is formed with the third wiringlayer, and the clock signal line can be formed with the second wiring.

Next, cross-sectional views taken along lines a-a′ and b-b′ in FIG. 28of the case of using a thin film transistor as a transistor will bedescribed with reference to FIGS. 29A and 29B. A structure shown inFIGS. 29A and 29B is provided with a substrate 120, a base film 121, afirst wiring layer 122, an insulating film 123, active layers 124 and125, a second wiring layer 126, an interlayer film 127, and a thirdwiring layer 129 as the structure shown in FIGS. 27A and 27B. Further,the structure shown in FIGS. 29A and 29B is provided with a contact 128a which connect the third wiring layer 129 and the second wiring layer126, and a contact 128 b which connects the third wiring layer 129 andthe first wiring layer 122.

Note that, in FIG. 29A, Reference numeral Ctft17 denotes a parasiticcapacitance element of the transistor 17, Cclk1 denotes a parasiticcapacitance element of the output terminal L and the first clock signalline CLK1, and Cclk2 denotes a parasitic capacitance element of theoutput terminal L and the second clock signal line CLK2 respectively.Reference numeral x in FIG. 29A denotes a width of the first wiringlayer over which the active layer or the second wiring layer exist inthe parasitic capacitance element Ctft17. Reference numeral y denotes adistance between the upper end of the first wiring layer and the lowerend of the second wiring layer in the parasitic capacitance elementsCclk1 and Cclk2.

Here, the capacitance value of the parasitic capacitance element Ctft17becomes larger as x is larger. Meanwhile, the capacitance values of theparasitic capacitance elements Cclk1 and Cclk2 become smaller as y islarger. When the capacitance value of the parasitic capacitance elementCtft17 is increased by making x larger as shown in FIG. 29A, parasiticcapacitance value associated with the electrode SR can be increased;thus, the electric potential of the electrode SR can be maintained at Hlevel sufficiently. Further, when the capacitance values of theparasitic capacitance elements Cclk1 and Cclk2 is reduced by making ylarger as in FIG. 29B, change in the electric potential of the outputterminal L due to change in the electric potentials of the first clocksignal line CLK1 and the second clock signal line CLK2 through theparasitic capacitance elements Cclk1 and Cclk2, can be reduced. Notethat thereupon, an active layer and a first wiring layer are notnecessarily formed below the first clock signal line CLK1 and the secondclock signal line CLK2. Further, the first clock signal line CLK1 andthe second clock signal line CLK2 may be formed with the first wiringlayer.

Next, description will be given of a top view of the case where crosscapacitance of the clock signal line and the output terminal L iseliminated so that the output terminal L is not affected by change inthe electric potential of the clock signal line as possible withreference to FIG. 30. The circuit 10 shown in the top view of FIG. 30 isprovided with transistors 11, 12, 13, 15, 16, and 17, a capacitorelement 14, a terminal P, an electrode SR, and an output terminal Las inFIG. 26 and FIG. 28, and the connections are also similar; however, thearrangement of the first clock signal line CLK1, the second clock signalline CLK2, and the transistors 11 and 12 is different form FIG. 26 andFIG. 28.

In FIG. 30, the power supply line Vss, the first clock signal line CLK1,and the second clock signal line CLK2 are formed from the second wiringlayer, and may be provided in substantially parallel to the directionwhere the circuits 10 extend (shown as 10 ext). Thus, in the case ofproviding a plurality of circuits 10, the length of leading the wiringis increased and wiring resistance is increased accordingly, and thus,malfunctions and increase in power consumption due to voltage drop ofthe power supply line can be prevented. Further, malfunctions caused bydistortion of a signal waveform, reduction in the range of voltage wherethe circuit operates normally can be suppressed.

The power supply line Vss, the first clock signal line CLK1, and thesecond clock signal line CLK2 may be provided outside elements formingthe circuit 10. Further, the power supply line Vss, and the first clocksignal line CLK1 and the second clock signal line CLK2 may be providedon the same side which is opposite to the side where the output terminalL is provided, with respect to the first transistor, the thirdtransistor, the second transistor, and the fourth transistor. Thus, theoutput terminal L can be prevented from crossing the first clock signalline CLK1 and the second clock signal line CLK2; thus, the power supplyline can be prevented from being affected by noise from the clock signalline, and malfunctions can be reduced.

Further, the channel length direction of the transistor 11 (shown asCh1) and the channel length direction of the transistor 12 (shown asCh2) may be substantially parallel. With this structure, the area of asubstrate occupied by the transistors 11 and 12 can be minimized, andcircuit scale can be reduced and generation of a region where the outputterminal L crosses the first clock signal line CLK1 and the second clocksignal line CLK2 can be prevented as well.

Embodiment Mode 5

In this embodiment mode, configuration examples of a display panel usinga shift register circuit of the present invention, described throughEmbodiment Modes 1 through 4, and a whole display device using the shiftregister circuit of the present invention will be described. Note thatin this specification, a display panel refers to a device for displayingstill images or moving images, which has a region in which pixels arearrayed (a pixel area) over a substrate such as a glass substrate, aplastic substrate, a quartz substrate, a silicon substrate. Further, adisplay device refers to a systematized device for displaying images onthe display panel, which has a circuit for converting electric signalsinputted from the external to data signals separately controlling theoptical states of the pixels, a driver circuit for dividing the datasignals by time and writing them into the pixels, or the like. Further,the display device may include a circuit for processing the data signalsthereby optimizing images to be displayed on the display panel, or thelike.

A shift register circuit of the present invention may be used as a partof a driver circuit forming a display device. Further, various methodcan be used for mounting a shift register circuit of the presentinvention to a display device, considering productivity, manufacturingcost, reliability, and the like. Here, examples of methods for mountinga shift register circuit of the present invention to a display devicewill be described with reference to FIGS. 31A to 31E.

FIG. 31A illustrates a display panel of the case where a data linedriver and a scan line driver that are a peripheral driver circuits areintegrated with a substrate provided with a pixel area. A display panel200 a shown in FIG. 31A includes a pixel area 201 a, a data line driver202 a, a scan line driver 203 a, and a connection wiring substrate 204a. The pixel area 201 a is a region in which pixels are arrayed; thepixel array may be a striped type or a delta type. Further, the pixelarea 201 a may include data signal lines which are wirings for writingdata signals separately controlling the optical states into the pixels.Further, the pixel area 201 a may include scan lines which are wiringsfor selecting pixel columns to which the data signals for separatelycontrolling the optical state.

The data line driver 202 a illustrates a circuit for controlling theelectrical states of the data signal lines in accordance with the imagesto be displayed on the pixel area 201 a. The data line driver 202 a mayhave a shift register circuit of the present invention so as to controla plurality of signal data lines by dividing them by the time division.

A scan line driver 203 a is a circuit for controlling the electricalstates of scan lines which are wirings for selecting pixel columns towhich the data signals for separately controlling the optical state. Thescan line driver 203 a may have a shift register circuit of the presentinvention for sequentially sequential scanning of a plurality of scanlines, selecting pixel columns to which the data signals for separatelycontrolling the optical state, and writhing the data signals into thepixels, thereby displaying images on the pixel area 201 a.

The connection wiring substrate 204 a is a substrate provided with awiring for connecting the display panel 200 a to an external circuit fordriving the display panel 200 a. When a connection wiring substrate 204a is formed from a flexible substrate of polyimide or the like, it iseasier to mount the display panel 200 a in a housing having a movableportion. Further, when the housing having the display panel 200 a isstrongly shocked, if the connection wiring substrate 204 a is flexible,the shock is absorbed by the connection wiring substrate 204 a; thus, arisk of disconnection by peel-off of the connection portion 205 a.

In the display panel 200 a shown in FIG. 31A, the data line driver 202 aand the scan line driver 203 a are integrated with the substrateprovided with the pixel area 201 a; thus, manufacturing cost can bereduced, and impact resistance can be increased because the number ofconnection points is small.

FIG. 31B illustrates a display panel of the case where a scan linedriver that is a peripheral driver circuit is integrated with asubstrate provided with the pixel area, and the data line driver isprovided as an IC manufactured on a single crystalline substrate overthe substrate and connected thereto (the method is also referred to asCOG). A display panel 200 b shown in FIG. 31B includes a pixel area 201b, a data line driver 202 b, a scan line driver 203 b, and a connectionwiring substrate 204 b.

The pixel area 201 b is a region in which pixels are arrayed; the pixelarray may be a striped type or a delta type. Further, the pixel area 201b may include data signal lines which are wirings for writing datasignals separately controlling the optical states into the pixels.Further, the pixel area 201 b may include scan lines which are wiringsfor selecting pixel columns to which the data signals for separatelycontrolling the optical state. The data line driver 202 b illustrates acircuit for controlling the electrical states of the data signal linesin accordance with the images to be displayed on the pixel area 201 b.The data line driver 202 b may have a shift register circuit of thepresent invention so as to control a plurality of signal data lines bydividing them by the time division.

A scan line driver 203 b is a circuit for controlling the electricalstates of scan lines which are wirings for selecting pixel columns towhich the data signals for separately controlling the optical state. Thescan line driver 2036 may have a shift register circuit of the presentinvention for sequentially sequential scanning of a plurality of scanlines, selecting pixel columns to which the data signals for separatelycontrolling the optical state, and writing the data signals into thepixels, thereby displaying images on the pixel area 201 b.

The connection wiring substrate 204 b is a substrate provided with awiring for connecting the display panel 200 b to an external circuit fordriving the display panel 2006. When a connection wiring substrate 204 bis formed from a flexible substrate of polyimide or the like, it iseasier to mount the display panel 200 b in a housing having a movableportion. Further, when the housing having the display panel 200 b isstrongly shocked, if the connection wiring substrate 204 b is flexible,the shock is absorbed by the connection wiring substrate 204 b; thus, arisk of disconnection by peel-off of the connection portion 205 b.

In the display panel 2006 shown in FIG. 31B, the scan line driver 203 bis integrated with the substrate provided with the pixel area 201 b;thus, manufacturing cost can be reduced, and impact resistance can beincreased because the number of connection points is small. Further,since an IC manufactured using a single crystal substrate is mounted asthe data line driver 202 b, the display panel can be manufactured withsignificantly little variation in the transistor characteristics; thus,yield of display devices can be improved. Further, since operatingvoltage can be reduced, power consumption can be reduced.

FIG. 31C illustrates a display panel of the case where a data linedriver and a scan line driver that are a peripheral driver circuits aremanufactured as an IC on a single crystal substrate over a substrateprovided with the pixel area, thereby achieving COG. A display panel 200c shown in FIG. 31C includes a pixel area 201 c, a data line driver 202c, a scan line driver 203 c, and a connection wiring substrate 204 c.

The pixel area 201 c is a region in which pixels are arrayed; the pixelarray may be a striped type or a delta type. Further, the pixel area 201c may include data signal lines which are wirings for writing datasignals separately controlling the optical states into the pixels.Further, the pixel area 201 c may include scan lines which are wiringsfor selecting pixel columns to which the data signals for separatelycontrolling the optical state.

The data line driver 202 c illustrates a circuit for controlling theelectrical states of the data signal lines in accordance with the imagesto be displayed on the pixel area 201 c. The data line driver 202 c mayhave a shift register circuit of the present invention so as to controla plurality of signal data lines by dividing them by the time division.

A scan line driver 203 c is a circuit for controlling the electricalstates of scan lines which are wirings for selecting pixel columns towhich the data signals for separately controlling the optical state. Thescan line driver 203 c may have a shift register circuit of the presentinvention for sequentially sequential scanning of a plurality of scanlines, selecting pixel columns to which the data signals for separatelycontrolling the optical state, and writhing the data signals into thepixels, thereby displaying images on the pixel area 201 c.

The connection wiring substrate 204 c is a substrate provided with awiring for connecting the display panel 200 c to an external circuit fordriving the display panel 200 c. When a connection wiring substrate 204c is formed from a flexible substrate of polyimide or the like, it iseasier to mount the display panel 200 c in a housing having a movableportion. Further, when the housing having the display panel 200 c isstrongly shocked, if the connection wiring substrate 204 c is flexible,the shock is absorbed by the connection wiring substrate 204 c; thus, arisk of disconnection by peel-off of the connection portion 205 c.

Further, since the display panel shown in FIG. 31C is mounted as an ICmanufactured using a single crystal substrate is mounted as the dataline driver 202 c and the scan line driver 203 c, the display panel canbe manufactured with significantly little variation in the transistorcharacteristics; thus, yield of display devices can be improved.Further, since operating voltage can be reduced, power consumption canbe reduced.

FIG. 31D illustrates a display panel of the case where a scan linedriver that is a peripheral driver circuit is integrated with a flexiblesubstrate provided with the pixel area, and the data line driver isprovided as an IC manufactured on a single crystalline substrate overthe flexible substrate and connected thereto(the method is also referredto as TAB). A display panel 200 d shown in FIG. 31D includes a pixelarea 201 d, a data line driver 202 d, a scan line driver 203 d, and aconnection wiring substrate 204 d.

The pixel area 201 d is a region in which pixels are arrayed; the pixelarray may be a striped type or a delta type. Further, the pixel area 201d may include data signal lines which are wirings for writing datasignals separately controlling the optical states into the pixels.Further, the pixel area 201 d may include scan lines which are wiringsfor selecting pixel columns to which the data signals for separatelycontrolling the optical state.

The data line driver 202 d illustrates a circuit for controlling theelectrical states of the data signal lines in accordance with the imagesto be displayed on the pixel area 201 d. The data line driver 202 d mayhave a shift register circuit of the present invention so as to controla plurality of signal data lines by dividing them by the time division.

A scan line driver 203 d is a circuit for controlling the electricalstates of scan lines which are wirings for selecting pixel columns towhich the data signals for separately controlling the optical state. Thescan line driver 203 d may have a shift register circuit of the presentinvention for sequentially sequential scanning of a plurality of scanlines, selecting pixel columns to which the data signals for separatelycontrolling the optical state, and writhing the data signals into thepixels, thereby displaying images on the pixel area 201 d.

The connection wiring substrate 204 d is a substrate provided with awiring for connecting the display panel 200 d to an external circuit fordriving the display panel 200 d. When a connection wiring substrate 204d is formed from a flexible substrate of polyimide or the like, it iseasier to mount the display panel 200 d in a housing having a movableportion. Further, when the housing having the display panel 200 d isstrongly shocked, if the connection wiring substrate 204 d is flexible,the shock is absorbed by the connection wiring substrate 204 d; thus, arisk of disconnection by peel-off of the connection portion 205 d.

In the display panel 200 d shown in FIG. 31D, the scan line driver 203 dis integrated with the substrate provided with the pixel area 201 d;thus, manufacturing cost can be reduced, and impact resistance can beincreased because the number of connection points is small. Further,since an IC manufactured using a single crystal substrate is mounted asthe data line driver 202 d, the display panel can be manufactured withsignificantly little variation in the transistor characteristics; thus,yield of display devices can be improved. Further, since operatingvoltage can be reduced, power consumption can be reduced. Further, sincethe data line driver 202 d is connected onto the connection wiringsubstrate 204 d, the region in the display panel 200 d other than thepixel area 201 d (also referred to as a frame) can be reduced, therebythe display device can have higher added value. Further, if theconnection wiring substrate 204 d is flexible, when the housing havingthe display panel 200 d is strongly shocked, the shock on the data linedriver 204 d is absorbed by the connection wiring substrate 204 d; thus,a risk of disconnection by peel-off of the data line driver 202 d fromthe connection wiring substrate 204 d.

FIG. 31E illustrates a display panel of the case where a data linedriver and a scan line driver that are peripheral driver circuits aremanufactured as ICs on a single crystalline substrate on a substrateprovided with the pixel area by TAB. A display panel 200 e shown in FIG.31E includes a pixel area 201 e, a data line driver 202 e, a scan linedriver 203 e, and a connection wiring substrate 204 e.

The pixel area 201 e is a region in which pixels are arrayed; the pixelarray may be a striped type or a delta type. Further, the pixel area 201e may include data signal lines which are wirings for writing datasignals separately controlling the optical states into the pixels.Further, the pixel area 201 e may include scan lines which are wiringsfor selecting pixel columns to which the data signals for separatelycontrolling the optical state.

The data line driver 202 e illustrates a circuit for controlling theelectrical states of the data signal lines in accordance with the imagesto be displayed on the pixel area 201 e. The data line driver 202 e mayhave a shift register circuit of the present invention so as to controla plurality of signal data lines by dividing them by the time division.

A scan line driver 203 e is a circuit for controlling the electricalstates of scan lines which are wirings for selecting pixel columns towhich the data signals for separately controlling the optical state. Thescan line driver 203 e may have a shift register circuit of the presentinvention for sequentially sequential scanning of a plurality of scanlines, selecting pixel columns to which the data signals for separatelycontrolling the optical state, and writhing the data signals into thepixels, thereby displaying images on the pixel area 201 e.

The connection wiring substrate 204 e is a substrate provided with awiring for connecting the display panel 200 e to an external circuit fordriving the display panel 200 e. When a connection wiring substrate 204e is formed from a flexible substrate of polyimide or the like, it iseasier to mount the display panel 200 e in a housing having a movableportion. Further, when the housing having the display panel 200 e isstrongly shocked, if the connection wiring substrate 204 e is flexible,the shock is absorbed by the connection wiring substrate 204 e; thus, arisk of disconnection by peel-off of the connection portion 205 e.

Since an IC manufactured using a single crystal substrate is mounted asthe data line driver 202 e and the scan line driver 203 e in the displaypanel 200 e shown in FIG. 31E, the display panel can be manufacturedwith significantly little variation in the transistor characteristics;thus, yield of display devices can be improved. Further, since operatingvoltage can be reduced, power consumption can be reduced. Further, sincethe data line driver 202 e is connected onto the connection wiringsubstrate 204 e, the frame of the display panel 200 e can be reduced,thereby the display device can have higher added value. Further, if theconnection wiring substrate 204 e is flexible, when the housing havingthe display panel 200 e is strongly shocked, the shock on the data linedriver 204 e is absorbed by the connection wiring substrate 204 e; thus,a risk of disconnection by peel-off of the data line driver 202 e andthe scan line driver 203 e from the connection wiring substrate 204 e.

Thus, a transistor of the invention may be any kinds of transistors andformed over any kinds of substrates. A shift register circuit if thepresent invention may be formed over a glass substrate, a plasticsubstrate, a single crystal substrate, an SOI substrate, or any othersubstrates. A part of the shift register circuit of the presentinvention may be formed over one substrate while another part of theshift register circuit of the present invention may be formed overanother substrate. That is, all the shift register circuits of thepresent invention are not required to be formed over the same substrate.

Next, a configuration example of a display device including a shiftregister circuit of the present invention will be described withreference to FIG. 32. A display device 220 shown in FIG. 32 is providedwith the display panel 200, the external driver circuit 221, and theconnection wiring substrate 204 shown in FIG. 31A to 31E.

The display panel 200 has a pixel area 201, a data line driver 202, anda scan line driver 203. Since the display panel 200 has been describedabove, the details will not be described here. However, naturally,display device 220 shown in FIG. 32, the data line driver 202 and thescan line driver 203 can be mounted by various methods.

The external driver circuit 221 includes a control circuit 210, an imagedata conversion circuit 211, and a power circuit 212. Further, the powercircuit 212 may be provided with a power supply CV for a control/imagedata conversion circuit, a power supply DV for drivers, a power supplyPV for a pixel circuit. Note that, the power supply PV for a pixelcircuit is not required to be provided in the power circuit 212depending on the configuration of the pixel area 201.

The connection wiring substrate 204 may be electrically connected to thedisplay panel 200 through a connection portion 205, and may beelectrically connected to the external driver circuit 221 through aconnector 213.

Further, in order to correspond to a display panel having a large pixelarea 201, as shown in FIG. 33, a plurality of data line drivers 202(202-1, 202-2, 202-3, and 202-4), a plurality of scan line drivers 203(203-1, 203-2, 203-3, and 203-4), a plurality of connection wiringsubstrates 204(204-1, 204-2, 204-3, 204-4, 204-5, 204-6, 204-7, and204-8) may be used for one display panel 200 and one pixel area 201.Here, in FIG. 33, the case of using four data line drivers 202 and fourscan line drivers 203 is shown as an example; however, the numbers ofthe data line drivers 202 and the scan line drivers 203 are not limitedin particular, and any number may be used. When the numbers of the dataline drivers 202 and the scan line drivers 203 are smaller, the numbersof ICs and connection points; thus, reliability can be improved andmanufacturing cost can be reduced. When the number of the data linedrivers 202 and the scan line drivers 203 are large, performancerequired for each driver is lowered, so that yield can be improved.

Note that the number of the connection wiring substrates 204 ispreferably two or more and the division number of the data line drivers202 and the scan line drivers 203 or less. When the number of theconnection wiring substrates 204 is larger than the division number ofthe drivers, the number of the contact points increases; thus, when thenumber of the contact points is increased, defects of breakage at thecontact points increases.

In FIG. 32, the control circuit 210 is connected to the image dataconversion circuit 211 and the power circuit 212. Further, the controlcircuit 210 is connected to the data line driver 202 and the scan linedriver 203 through the connector 213, the connection wiring substrate204, and the connection portion 205. Further, the image data conversioncircuit 211 is connected to an input terminal which inputs image data.Further, the image data conversion circuit 211 is connected to the dataline driver 202 through the connector 213, the connection wiringsubstrate 204, and the connection portion 205.

Further, the power circuit 212 supplies power for each circuit, and thepower supply CV for control/image data conversion circuit in the powercircuit 212 is connected to the control circuit 210 and the image dataconversion circuit 211 the power supply DV for drivers is connected tothe data line driver 202 and the scan line driver 203 through theconnector 213, the connection wiring substrate 204, and the connectionportion 205; the power supply PV for a pixel circuit is connected to thepixel area 201 through the connector 213, the connection wiringsubstrate 204, and the connection portion 205.

The voltage supplied to the control circuit 210 and the image dataconversion circuit 211 from the power supply CV is preferably as low aspossible since they control circuit 210 and the image data conversioncircuit 211 conduct the logic operations, and thus, it is desirablyabout 3 V. Further, the voltage supplied from the power supply DV fordrivers is preferably as low as possible in order to reduce powerconsumption. For example, when the ICs are used for the data line driver202 and the scan line driver 203, the voltage is desirably about 3 V.Further, the data line driver 202 and the scan line driver 203 isintegrated with the display panel 200, voltage having an amplitude ofabout twice to three times as high as the threshold voltage of thetransistor is desirably supplied. Thus, the circuit can be operatedsecurely while suppressing increase in power consumption.

The control circuit 210 may have a configuration such that an operationof generating clocks to be supplied to data line driver 202 and the scanline driver 95, an operation of generating and supplying timing pulses,or the like are conducted. In addition, the control circuit 210 may havea configuration such that an operation of generating clocks to besupplied to the image data conversion circuit, an operation ofgenerating timing pulses outputting converted image data to the dataline driver 202, or the like are conducted. The power circuit 212 mayhave a configuration such that an operation of stopping supply ofvoltage to each circuit when the image data conversion circuit 211, thedata line driver 202, and the scan line driver 203, for example, are notrequired to be operated, thereby reducing power consumption.

When image data is inputted to the image data conversion circuit 211,the image data conversion circuit 211 converts the image data into datawhich can be inputted to the data line driver 202 in accordance with thetiming at which a signal is supplied from the control circuit 210, andthen, outputs the data to the data line driver circuit 202.Specifically, a configuration may be used in which image data input withan analog signal is converted into a digital signal with the imageconversion circuit 211, and then, image data of the digital signal isoutput to the data line driver 202.

The data line driver 202 may have a configuration such as to operate theshift register of the present invention in accordance with a clocksignal and a timing pulse supplied from the control circuit 210; take inthe image data inputted to the data line driver 202 with time division;and output a data voltage or a data current with an analog value to aplurality of the data lines in accordance with the data which has beentaken. Updating of the data voltage or the data current output to thedata lines may be conducted by a latch pulse supplied from the controlcircuit 210. Further, in order to reset the shift register circuit ofthe present invention, a signal for the reset operation may be inputted.Further, in order to apply reverse bias to the transistors in the shiftregister circuit of the present invention, a signal for applying reversebias can be inputted.

In accordance with the updating of the data voltage or the data currentoutput to the data lines, the scan line driver 203 operates the shiftregister of the present invention in response to a clock signal and atiming pulse supplied from the control circuit 210 to scan scan lines 29sequentially. Here, in order to reset the shift register circuit of thepresent invention, a signal for the reset operation may be inputted.Further, in order to apply reverse bias to the transistors in the shiftregister circuit of the present invention, a signal for applying reversebias can be inputted.

Note that examples of disposing the scan line driver 203 on one side areillustrated in FIG. 32 and FIG. 33; however, the scan line driver 203may be disposed on each side instead of one side. In the case ofdisposing the scan line driver 203 on each side, left-right balance ofthe display device is achieved when mounted on an electronic device, sothat it is advantageous in increasing the degree of freedom forarrangement.

Embodiment Mode 6

In this embodiment mode, electronic devices which can be realized byusing a shift register circuit of the present invention will bedescribed with reference to FIGS. 34A to 34H.

The present invention can be applied to various electronic devices.Specifically the present invention can be applied to display devices ofelectronic devices. As such electronic devices, a camera such as a videocamera and a digital camera; a goggle type display; a navigation system;an audio reproducing device (car audio, an audio component, or thelike); a computer; a game machine; a portable information terminal (amobile computer, a cellular phone, a portable game machine, anelectronic book, or the like); an image reproducing device including arecording medium (specifically, a device capable of reproducing thecontent of a recording medium such as a digital versatile disc (DVD) andhaving a display device that can display the image of the data); and thelike can be listed.

FIG. 34A shows a television receiver machine including a housing 3001, asupporting stand 3002, a display area 3003, speaker units 3004, a videoinput terminal 3005, and the like. A display device of the presentinvention can be applied to the display area 3003. For example, since alarge display area is demanded for a television receiver, a displaydevice shown in FIG. 33. Note that display devices include, amongothers, all light emitting devices used for displaying information, forexample, for a personal computer, for TV broadcast reception, or foradvertisement display. A display device using a shift register circuitof the present invention can be used for the display area 3003, therebyobtaining a highly reliable electronic device, which hardly malfunctionseven when subjected to noise such as external electromagnetic waves, andin which reverse bias application can be operated.

FIG. 34B shows a digital camera including a main body 3101, a displayarea 3102, an image receiving portion 3103, operation keys 3104, anexternal connection port 3105, a shutter 3106, and the like. A displaydevice using a shift register circuit of the present invention can beused for the display area 3102, thereby obtaining a highly reliabledigital camera, which hardly malfunctions even when subjected to noisesuch as external electromagnetic waves, and in which reverse biasapplication can be operated.

FIG. 34C shows a computer including a main body 3201, a housing 3202, adisplay area 3203, a keyboard 3204, an external connection port 3205, apointing mouse 3206, and the like. A display device using a shiftregister circuit of the present invention can be used for the displayarea 3203, thereby obtaining a highly reliable computer, which hardlymalfunctions even when subjected to noise such as externalelectromagnetic waves, and in which reverse bias application can beoperated.

FIG. 34D shows a mobile computer including a main body 3301, a displayarea 3302, a switch 3303, operation keys 3304, an infrared port 3305,and the like. A display device using a shift register circuit of thepresent invention can be used for the display area 3302, therebyobtaining a highly reliable mobile computer, which hardly malfunctionseven when subjected to noise such as external electromagnetic waves, andin which reverse bias application can be operated.

FIG. 34E shows a mobile image reproduction device equipped with arecording medium (DVD, and the like) (specifically, a DVD reproductiondevice) including a main body 3401, a housing 3402, a display area A3403, a display area B 3404, a recording-medium reader portion 3405, anoperation key 3406, a speaker unit 3407, and the like. The display areaA 3403 mainly displays image information, while the display area B 3404mainly displays text information. A display device using a shiftregister circuit of the present invention can be used for the displayarea A3403 and the display area B3404, thereby obtaining a highlyreliable image reproduction device, which hardly malfunctions even whensubjected to noise such as external electromagnetic waves, and in whichreverse bias application can be operated.

FIG. 34F shows a goggle type display including a main body 3501, adisplay area 3502, and an arm portion 3503. The goggle type display canbe manufactured by applying a display device described in any one of theabove embodiment modes to the display area 3502. A display device usinga shift register circuit of the present invention can be used for thedisplay area 3502, thereby obtaining a highly reliable goggle typedisplay, which hardly malfunctions even when subjected to noise such asexternal electromagnetic waves, and in which reverse bias applicationcan be operated.

FIG. 34G shows a video camera including a main body 3601, a display area3602, a housing 3603, an external connection port 3604, a remotecontroller receiving portion 3605, an image receiving portion 3606, abattery 3607, an audio input portion 3608, operation keys 3609, and thelike. A display device using a shift register circuit of the presentinvention can be used for the display area 3602, thereby obtaining ahighly reliable video camera, which hardly malfunctions even whensubjected to noise such as external video camera, and in which reversebias application can be operated.

FIG. 34H shows a cellular phone including a main body 3701, a housing3702, a display area 3703, an audio input portion 3704, an audio outputportion 3705, an operation key 3706, an external connection port 3707,an antenna 3708, and the like. A display device using a shift registercircuit of the present invention can be used for the display area 3703,thereby obtaining a highly reliable cellular phone, which hardlymalfunctions even when subjected to noise such as external cellularphone, and in which reverse bias application can be operated.

Thus, the present invention can be applied to electronic devices in allfields.

This application is based on Japanese Patent Application serial no.2005-378262 filed in Japan Patent Office on Dec. 28, 2005, the entirecontents of which are hereby incorporated by reference.

1. A semiconductor device comprising: a first transistor; a second transistor; and an element configured to do a diode operation; wherein a source or a drain of the first transistor is connected to a gate of the second transistor, wherein the gate of the first transistor is connected to a positive electrode of the element, and wherein the gate of the second transistor is connected to a negative electrode of the element. 